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1

Effects of different gas phases and gas bubbles on the nucleation kinetics.  

PubMed

In this study, the effects of different gas phases and gas bubbles on the Induction time were investigated. In the first step, the effects of different kinds of gases (N(2), Ar, dry air-N(2) and dry air-Ar) which are fed into solution-gas interphase and into the solution were determined. After determining the most effective gas upon the Induction time, the next step was to use this gas in the presence of the seed crystals, to specify variation in the Induction time. The experimental results show that gassing and the presence of seed crystal tend to shorten the Induction time as compared to the normal crystallization condition. PMID:25125123

Ceyhan, Ayhan Abdullah; Baytar, Orhan; Pehlivan, Erol

2014-01-01

2

Pore-scale interfacial dynamics during gas-supersaturated water injection in porous media - on nucleation, growth and advection of disconnected fluid phases (Invited)  

NASA Astrophysics Data System (ADS)

Degassing and in situ development of a mobile gas bubbles occur when injecting supersaturated aqueous phase into water-saturated porous media. Supersaturated water injection (SWI) has potentially significant applications in remediation of soils contaminated by non-aqueous phase liquids and in enhanced oil recovery. Pore network simulations indicate the formation of a region near the injection boundary where gas phase nuclei are activated and grow by mass transfer from the flowing supersaturated aqueous phase. Ramified clusters of gas-filled pores develop which, owing to the low prevailing Bond number, grow laterally to a significant extent prior to the onset of mobilization, and are thus likely to coalesce. Gas cluster mobilization invariably results in fragmentation and stranding, such that a macroscopic region containing few tenuously connected large gas clusters is established. Beyond this region, gas phase nucleation and mass transfer from the aqueous phase are limited by diminishing supply of dissolved gas. New insights into SWI dynamics are obtained using rapid micro-visualization in transparent glass micromodels. Using high-speed imaging, we observe the nucleation, initial growth and subsequent fate (mobilization, fragmentation, collision, coalescence and stranding) of CO2 bubbles and clusters of gas-filled pores and analyze cluster population statistics. We find significant support for the development of invasion-percolation-like patterns, but also report on hitherto unaccounted for gas bubble behavior. Additionally, we report for the first time on the acoustic emission signature of SWI in porous media and relate it to the dynamics of bubble nucleation and growth. Finally, we identify the pore-scale mechanisms associated with the mobilization and subsequent recovery of a residual non-aqueous phase liquid due to gas bubble dynamics during SWI.

Or, D.; Ioannidis, M.

2010-12-01

3

Evolution of gas saturation and relative permeability during gas production from hydrate-bearing sediments: Gas invasion vs. gas nucleation  

NASA Astrophysics Data System (ADS)

and both gas and water permeabilities change as a function of gas saturation. Typical trends established in the discipline of unsaturated soil behavior are used when simulating gas production from hydrate-bearing sediments. However, the evolution of gas saturation and water drainage in gas invasion (i.e., classical soil behavior) and gas nucleation (i.e., gas production) is inherently different: micromodel experimental results show that gas invasion forms a continuous flow path while gas nucleation forms isolated gas clusters. Complementary simulations conducted using tube networks explore the implications of the two different desaturation processes. In spite of their distinct morphological differences in fluid displacement, numerical results show that the computed capillarity-saturation curves are very similar in gas invasion and nucleation (the gas-water interface confronts similar pore throat size distribution in both cases); the relative water permeability trends are similar (the mean free path for water flow is not affected by the topology of the gas phase); and the relative gas permeability is slightly lower in nucleation (delayed percolation of initially isolated gas-filled pores that do not contribute to gas conductivity). Models developed for unsaturated sediments can be used for reservoir simulation in the context of gas production from hydrate-bearing sediments, with minor adjustments to accommodate a lower gas invasion pressure Po and a higher gas percolation threshold.

Jang, Jaewon; Santamarina, J. Carlos

2014-01-01

4

On martensitic phase nucleation with surface effects  

NASA Astrophysics Data System (ADS)

C ONTINUUM treatments of martensitic phase transitions are capable of accounting for a variety of surface effects caused by the interaction of coexisting phases of a material. Such phenomena are thought to play a critical role in determining the size, shape and stability of nucleated embryos as well as to affect the conditions under which nucleation occurs. These issues are examined within a purely mechanical context with the interaction modeled by traction and energy fields defined on the interface between phases. A class of isotropic, hyperelastic materials is introduced that is capable of modeling the dilatational component of martensitic phase transformations. Such materials are considered in a noninertial, axisymmetric setting that provides a means of exploring a variety of surface effects. Here nucleation events are modeled as deterministic, temporal shocks that are global in spatial extent, and a criterion for nucleation is suggested that is based on the energy available to create an embryo composed of a new phase. The model presented does more than capture the desired surface effects. It shows how they are related to specific assumptions regarding the constitution of interfaces. Three different types of interface are presented that serve to illustrate this.

Lusk, Mark

1994-02-01

5

Nucleation and growth of Nb nanoclusters during plasma gas condensation  

SciTech Connect

Niobium nanoclusters were produced using a plasma gas condensation process. The influence of gas flow rate, aggregation length, and source current on the nanocluster nucleation and growth were analyzed. Nanoclusters with an average diameter from 4 nm to 10 nm were produced. Cluster size and concentration were tuned by controlling the process inputs. The effects of each parameter on the nucleation zone, growth length, and residence time was examined. The parameters do not affect the cluster formation and growth independently; their influence on cluster formation can be either cumulative or competing. Examining the nucleation and growth over a wide combination of parameters provided insight into their interactions and the impact on the growth process. These results provide the opportunity for a broader understanding into the nucleation and growth of nanoclusters and some insights into how process parameters interact during deposition. This knowledge will enhance the ability to create nanoclusters with desired size dispersions.

Bray, K. R.; Jiao, C. Q. [UES, Inc., 4401 Dayton-Xenia Rd, Dayton, Ohio 45432 (United States)] [UES, Inc., 4401 Dayton-Xenia Rd, Dayton, Ohio 45432 (United States); DeCerbo, J. N. [Air Force Research Laboratory, AFRL/RQQE, 1950 Fifth St., WPAFB, Ohio 45433 (United States)] [Air Force Research Laboratory, AFRL/RQQE, 1950 Fifth St., WPAFB, Ohio 45433 (United States)

2013-06-21

6

Phase equilibrium and nucleation in VLS-grown nanowires.  

PubMed

Phase diagrams accounting for capillarity and surface stress in VLS-grown nanowires have been calculated, and linearized forms for the compositions of the solid and liquid are given. The solid-vapor interfacial energy causes a significant depression of the liquidus, and the impurity concentration in the wire decreases with decreasing wire diameter. Nucleation calculations give upper bounds on the nucleation temperature and liquid supersaturation during growth that are consistent with measurements in the Au-Ge system. PMID:18954122

Schwalbach, Edwin J; Voorhees, Peter W

2008-11-01

7

Nucleation  

PubMed Central

Crystallization starts with nucleation and control of nucleation is crucial for the control of the number, size, perfection, polymorphism and other characteristics of crystalline materials. This is particularly true for crystallization in solution, which is an essential part of processes in the chemical and pharmaceutical industries and a major step in physiological and pathological phenomena. There have been significant recent advances in the understanding of the mechanism of nucleation of crystals in solution. The foremost of these are the two-step mechanism of nucleation and the notion of the solution–crystal spinodal. According to the two-step mechanism, the crystalline nucleus appears inside pre-existing metastable clusters of size several hundred nanometers, which consist of dense liquid and are suspended in the solution. While initially proposed for protein crystals, the applicability of this mechanism has been demonstrated for small molecule organic materials, colloids, polymers, and biominerals. This mechanism helps to explain several long-standing puzzles of crystal nucleation in solution: nucleation rates which are many orders of magnitude lower than theoretical predictions, the significance of the dense protein liquid, and others. At high supersaturations typical of most crystallizing systems, the generation of crystal embryos occurs in the spinodal regime, where the nucleation barrier is negligible. The solution-crystal spinodal helps to understand the role of heterogeneous substrates in nucleation and the selection of crystalline polymorphs. Importantly, these ideas provide powerful tools for control of the nucleation process by varying the solution thermodynamic parameters. PMID:21132117

Vekilov, Peter G.

2010-01-01

8

Colloidal gas-liquid transition: tuning nucleation and growth by Critical Casimir forces  

NASA Astrophysics Data System (ADS)

The nucleation and growth of the liquid phase has been well studied in simulations, but direct experimental observations remain challenging. Here we present a detailed study of the colloidal gas-liquid transition induced by Critical Casimir forces that allow direct control over particle interactions via temperature-dependent solvent fluctuations. We show that with the direct control over particle interactions we can ``freeze'' a dilute colloidal gas into a dense colloidal liquid. By using dynamic light scattering to follow the evolution of liquid aggregates we observe three clearly distinct regimes: nucleation, interface limited- and diffusion limited growth. We elucidate these regimes directly in real space by using confocal microscopy. In the nucleation regime, we determine the Gibbs free energy, interfacial tension and chemical potential of the liquid aggregates directly from their size distribution. In the growth regime, we can directly follow the attachment of particles, and the collapse of liquid aggregates to large drops. Our critical Casimir colloidal system allows us to control all stages of nucleation and growth with temperature, thereby providing unprecedented insight into this gas-liquid transition.

Nguyen, Duc; Schall, Peter

2012-02-01

9

Nucleation of the diamond phase in aluminium-solid solutions  

NASA Technical Reports Server (NTRS)

Precipitation was studied from fcc solid solutions with silicon, germanium, copper and magnesium. Of all these elements only silicon and germanium form diamond cubic (DC) precipitates in fcc Al. Nucleation of the DC structure is enhanced if both types of atom are dissolved in the fcc lattice. This is interpreted as due to atomic size effects in the prenucleation stage. There are two modes of interference of fourth elements with nucleation of the DC phase in Al + Si, Ge. The formation of the DC phase is hardly affected if the atoms (for example, copper) are rejected from the (Si, Ge)-rich clusters. If additional types of atom are attracted by silicon and/or germanium, DC nuclei are replaced by intermetallic compounds (for example Mg2Si).

Hornbogen, E.; Mukhopadhyay, A. K.; Starke, E. A., Jr.

1993-01-01

10

Observing classical nucleation theory at work by monitoring phase transitions with molecular precision  

PubMed Central

It is widely accepted that many phase transitions do not follow nucleation pathways as envisaged by the classical nucleation theory. Many substances can traverse intermediate states before arriving at the stable phase. The apparent ubiquity of multi-step nucleation has made the inverse question relevant: does multistep nucleation always dominate single-step pathways? Here we provide an explicit example of the classical nucleation mechanism for a system known to exhibit the characteristics of multi-step nucleation. Molecular resolution atomic force microscopy imaging of the two-dimensional nucleation of the protein glucose isomerase demonstrates that the interior of subcritical clusters is in the same state as the crystalline bulk phase. Our data show that despite having all the characteristics typically associated with rich phase behaviour, glucose isomerase 2D crystals are formed classically. These observations illustrate the resurfacing importance of the classical nucleation theory by re-validating some of the key assumptions that have been recently questioned. PMID:25465441

Sleutel, Mike; Lutsko, Jim; Van Driessche, Alexander E.S.; Durán-Olivencia, Miguel A.; Maes, Dominique

2014-01-01

11

Observing classical nucleation theory at work by monitoring phase transitions with molecular precision  

NASA Astrophysics Data System (ADS)

It is widely accepted that many phase transitions do not follow nucleation pathways as envisaged by the classical nucleation theory. Many substances can traverse intermediate states before arriving at the stable phase. The apparent ubiquity of multi-step nucleation has made the inverse question relevant: does multistep nucleation always dominate single-step pathways? Here we provide an explicit example of the classical nucleation mechanism for a system known to exhibit the characteristics of multi-step nucleation. Molecular resolution atomic force microscopy imaging of the two-dimensional nucleation of the protein glucose isomerase demonstrates that the interior of subcritical clusters is in the same state as the crystalline bulk phase. Our data show that despite having all the characteristics typically associated with rich phase behaviour, glucose isomerase 2D crystals are formed classically. These observations illustrate the resurfacing importance of the classical nucleation theory by re-validating some of the key assumptions that have been recently questioned.

Sleutel, Mike; Lutsko, Jim; van Driessche, Alexander E. S.; Durán-Olivencia, Miguel A.; Maes, Dominique

2014-12-01

12

IMPORTANCE OF PHASE CHANGES IN TITAN'S LOWER ATMOSPHERE. TOOLS FOR THE STUDY OF NUCLEATION  

E-print Network

IMPORTANCE OF PHASE CHANGES IN TITAN'S LOWER ATMOSPHERE. TOOLS FOR THE STUDY OF NUCLEATION L. Guez, cloud opacity and could be influenced by latent heat exchange. A rudimentary model with no methane in a model of phase changes. The suspicion of difficult methane nucleation comes from analysis of Voyager

Boyer, Edmond

13

Electron diffraction data on nucleation and growth of an hcp phase in homogeneous (Ar) and heterogeneous (Ar-Kr) clusters  

NASA Astrophysics Data System (ADS)

The nucleation and growth of the hcp phase in homogeneous (Ar) and heterogeneous (Ar-Kr) clusters formed in adiabatically expanding supersonic jets of the inert gases are studied by electron diffraction. The average size of the clusters ranges from 2 × 103 to 1 × 105 atoms/cluster. A threshold size of the clusters is found at which an hcp phase forms along with the fcc structure. The relative amount of the hcp phase in the single crystal clusters increases with their size. The relative volume of the hcp phase in the heterogeneous clusters exceeds that in homogeneous clusters of the same size. A correlation is established between the relative volume of the hcp phase in the clusters and the number of "defect" planes contained in the fcc matrix from which hcp phase nucleates. It is found that in very large (? ? 150 Å) polycrystalline aggregations the fraction of the hcp phase reaches a maximum and does not increase as the clusters become larger. A mechanism is proposed for the nucleation and growth of the hcp phase in inert gas clusters.

Danylchenko, O. G.; Kovalenko, S. I.; Konotop, O. P.; Samovarov, V. N.

2014-12-01

14

Gas-liquid nucleation of nonideal binary mixtures. I. A density functional study  

Microsoft Academic Search

The binary gas–liquid nucleation of model Lennard-Jones mixtures is studied using density functional methods. It is shown that the ordinary ‘‘Ar’’–‘‘Kr’’ mixture shows stronger nonclassical nucleation behavior than previously thought. A more nonideal mixture is defined by modifying the usual mixing rules of the Lennard-Jones parameters. This fluid exhibits significantly stronger surface activity than the ordinary mixture. As with water\\/alcohol

Ari Laaksonen; David W. Oxtoby

1995-01-01

15

Propandiol vapor nucleation rates  

NASA Astrophysics Data System (ADS)

Consideration of vapor-gas nucleation as binary vapor nucleation (instead widely used the one component approximation for nucleation of this system now) may lead the progress in the development of nucleation theory. Observations of phase transitions initiated by the carrier gas in the critical embryos of condensate can be a sufficiently convincing argument in this discussion. In order to confirm the role of the carrier gases received in the recent research1, in present study 1,2-propanediol and 1,3-propanediol vapor nucleation rates were measured. Carbon dioxide (Tc=304.2 K,Pc=7.39 MPa) and sulfur hexafluoride (Tc=318.7 K,Pc=3.75 MPa) were chosen as the carrier gases, because of their low and convenient critical temperatures, Tc, and critical pressures, Pc. Analysis of the experimental data shows that gas-carrier molecules are involved in new phase embryo formation. Vapor nucleation of investigated substances in a carrier gas atmosphere can be considered as nucleation of binary system.

Anisimov, M. P.; Nasibulin, A. G.; Timoshina, L. V.; Koropchak, J. A.

2000-08-01

16

Memory effect on the pressure-temperature condition and induction time of gas hydrate nucleation  

Microsoft Academic Search

The focus of this study is to investigate the influence of memory effect and the relation of its existence with the dissociation temperature, using gas hydrate formation and dissociation experiments. This is beneficial because memory effect is considered as an effective approach to promote the thermodynamic and dynamic conditions of gas hydrate nucleation. Seven experimental systems (twenty tests in total)

Qiang Wu; Baoyong Zhang

2010-01-01

17

Gas Phase Nanoparticle Integration  

Microsoft Academic Search

We report on two gas phase nanoparticle integration processes to assemble nanomaterials onto desired areas on a substrate. We expect these processes to work with any material that can be charged. The processes offer self- aligned integration and could be applied to any nanomaterial device requiring site specific assembly. The Coulomb force process directs the assembly of nanoparticles onto charged

Chad R. Barry; Heiko O. Jacobs

2007-01-01

18

Exploring the discrepancies between experiment, theory, and simulation for the homogeneous gas-to-liquid nucleation of 1-pentanol  

NASA Astrophysics Data System (ADS)

Using an efficient Monte Carlo approach known as Aggregation-Volume-bias Monte Carlo with self-adaptive Umbrella Sampling and Histogram Reweighting (AVUS-HR), we obtained the nucleation free energy profile of 1-pentanol at various temperatures from 220 to 360 K. From these profiles, differences between the free energy barrier heights obtained from our simulations and those predicted by the classical nucleation theory (CNT) were calculated. Our results strongly support that the logarithm of the nucleation rate ratio between simulation (or experiment) and CNT increases almost linearly with the inverse temperature. Among the various factors that contribute to the discrepancy between simulation and CNT nucleation rates, the nonzero surface free energy of the monomer included in the CNT makes the largest contribution. On the molecular level, the simulations indicate that a gas-phase cluster of 1-pentanol molecules is relatively compact and can contain multiple hydrogen bonded aggregates of various sizes and that this aggregate size distribution depends strongly on temperature and also on the overall size of the cluster system.

Nellas, Ricky B.; Keasler, Samuel J.; Siepmann, J. Ilja; Chen, Bin

2010-04-01

19

Nonequilibrium thermodynamics of nucleation.  

PubMed

We present a novel approach to nucleation processes based on the GENERIC framework (general equation for the nonequilibrium reversible-irreversible coupling). Solely based on the GENERIC structure of time-evolution equations and thermodynamic consistency arguments of exchange processes between a metastable phase and a nucleating phase, we derive the fundamental dynamics for this phenomenon, based on continuous Fokker-Planck equations. We are readily able to treat non-isothermal nucleation even when the nucleating cores cannot be attributed intensive thermodynamic properties. In addition, we capture the dynamics of the time-dependent metastable phase being continuously expelled from the nucleating phase, and keep rigorous track of the volume corrections to the dynamics. Within our framework the definition of a thermodynamic nuclei temperature is manifest. For the special case of nucleation of a gas phase towards its vapor-liquid coexistence, we illustrate that our approach is capable of reproducing recent literature results obtained by more microscopic considerations for the suppression of the nucleation rate due to nonisothermal effects. PMID:25494727

Schweizer, M; Sagis, L M C

2014-12-14

20

Nonequilibrium thermodynamics of nucleation  

NASA Astrophysics Data System (ADS)

We present a novel approach to nucleation processes based on the GENERIC framework (general equation for the nonequilibrium reversible-irreversible coupling). Solely based on the GENERIC structure of time-evolution equations and thermodynamic consistency arguments of exchange processes between a metastable phase and a nucleating phase, we derive the fundamental dynamics for this phenomenon, based on continuous Fokker-Planck equations. We are readily able to treat non-isothermal nucleation even when the nucleating cores cannot be attributed intensive thermodynamic properties. In addition, we capture the dynamics of the time-dependent metastable phase being continuously expelled from the nucleating phase, and keep rigorous track of the volume corrections to the dynamics. Within our framework the definition of a thermodynamic nuclei temperature is manifest. For the special case of nucleation of a gas phase towards its vapor-liquid coexistence, we illustrate that our approach is capable of reproducing recent literature results obtained by more microscopic considerations for the suppression of the nucleation rate due to nonisothermal effects.

Schweizer, M.; Sagis, L. M. C.

2014-12-01

21

Gravitationally compact objects as nucleation sites for first-order vacuum phase transitions  

NASA Astrophysics Data System (ADS)

A characteristic of first-order phase transitions is their ability to be initiated by nucleation sites. In this paper we consider the role that gravitationally compact objects may play as nucleation sites for first-order phase transitions within quantum fields. As the presence of nucleation sites may prevent the onset of supercooling, the existence of nucleation sites for phase transitions within quantum fields may play an important role in some inflationary models of the Universe, in which the Universe is required to exist in a supercooled state for a period of time. In this paper we calculate the Euclidean action for an O(3) bubble nucleating about a gravitationally compact object, taken to be a boson star for simplicity. The gravitational field of the boson star is taken to be a small perturbation on flat space, and the O(3) action is calculated to linear order as a perturbation on the O(4) action. The Euclidean bubble profile is found by solving the (Higgs) scalar field equation numerically; the thin-wall approximation is not used. The gravitationally compact objects are found to have the effect of reducing the Euclidean action of the nucleating bubble, as compared to the Euclidean action for the bubble in flat spacetime. The effect is strongest when the size of the gravitationally compact object is comparable to the size of the nucleating bubble. Further, the size of the decrease in action increases as the nucleating ``star'' is made more gravitationally compact. Thus, gravitationally compact objects may play the role of nucleation sites. However, their importance to the process of false-vacuum decay is strongly dependent upon their number density within the Universe.

Samuel, David A.; Hiscock, William A.

1992-06-01

22

Nucleation of ordered solid phases of proteins via a disordered high-density state: Phenomenological approach  

NASA Astrophysics Data System (ADS)

Nucleation of ordered solid phases of proteins triggers numerous phenomena in laboratory, industry, and in healthy and sick organisms. Recent simulations and experiments with protein crystals suggest that the formation of an ordered crystalline nucleus is preceded by a disordered high-density cluster, akin to a droplet of high-density liquid that has been observed with some proteins; this mechanism allowed a qualitative explanation of recorded complex nucleation kinetics curves. Here, we present a simple phenomenological theory that takes into account intermediate high-density metastable states in the nucleation process. Nucleation rate data at varying temperature and protein concentration are reproduced with high fidelity using literature values of the thermodynamic and kinetic parameters of the system. Our calculations show that the growth rate of the near-critical and supercritical ordered clusters within the dense intermediate is a major factor for the overall nucleation rate. This highlights the role of viscosity within the dense intermediate for the formation of the ordered nucleus. The model provides an understanding of the action of additives that delay or accelerate nucleation and presents a framework within which the nucleation of other ordered protein solid phases, e.g., the sickle cell hemoglobin polymers, can be analyzed.

Pan, Weichun; Kolomeisky, Anatoly B.; Vekilov, Peter G.

2005-05-01

23

Role of Dynamic Nucleation at Moving Boundaries in Phase and Microstructure Selection  

NASA Technical Reports Server (NTRS)

Solidification microstructures that form under steady-state growth conditions (cells, dendrites, regular eutectics, etc.) are reasonably well understood in comparison to other, more complex microstructures, which form under intrinsically non-steady-state growth conditions due to the competition between the nucleation and growth of several phases. Some important practical examples in this latter class include microstructures forming in peritectic systems in highly undercooled droplets, and in strip cast stainless steels. Prediction of phase and microstructure selection in these systems has been traditionally based on (1) heterogeneous nucleation on a static interface, and (2) comparing the relative growth rate of different phase/microstructures under steady-state growth conditions. The formation of new phases, however, occurs via nucleation on, or ahead of, a moving boundary. In addition, the actual selection process is controlled by a complex interaction between the nucleation process and the growth competition between the nuclei and the pre-existing phase under non-steady-state conditions. As a result, it is often difficult to predict which microstructure will form and which phases will be selected under prescribed processing conditions. This research addresses this critical role of nucleation at moving boundaries in the selection of phases and solidification microstructures through quantitative experiments and numerical modeling in peritectic systems. In order to create a well characterized system in which to study this problem, we focus on the directional solidification of hypo- and hyper-peritectic alloys in the two-phase region, imposing a large enough ratio of temperature gradient/growth rate (G/V(sub p)) to suppress the morphological instability of both the parent (alpha) and peritectic (Beta) phases, i.e. each phase alone would grow as a planar front. Our combined experimental and theoretical results show that, already in this simplified case, the growth competition of these two phases leads to a rich variety of microstructures that depend sensitively upon the relative importance of nucleation, diffusion, and convection.

Karma, Alain; Trivedi, Rohit

1999-01-01

24

Localized Orientational Order Chaperones the Nucleation of Rotator Phases in Hard Polyhedral Particles  

NASA Astrophysics Data System (ADS)

The nucleation kinetics of the rotator phase in hard cuboctahedra, truncated octahedra, and rhombic dodecahedra is simulated via a combination of forward flux sampling and umbrella sampling. For comparable degrees of supersaturation, the polyhedra are found to have significantly lower free-energy barriers and faster nucleation rates than hard spheres. This difference primarily stems from localized orientational ordering, which steers polyhedral particles to pack more efficiently. Orientational order hence fosters here the growth of orientationally disordered nuclei.

Thapar, Vikram; Escobedo, Fernando A.

2014-01-01

25

Ice nucleation by combustion ash particles at conditions relevant to mixed-phase clouds  

NASA Astrophysics Data System (ADS)

Ice nucleating particles can modify cloud properties with implications for climate and the hydrological cycle; hence, it is important to understand which aerosol particle types nucleate ice and how efficiently they do so. It has been shown that aerosol particles such as natural dusts, volcanic ash, bacteria and pollen can act as ice nucleating particles, but the ice nucleating ability of combustion ashes has not been studied. Combustion ashes are major by-products released during the combustion of solid fuels and a significant amount of these ashes are emitted into the atmosphere either during combustion or via aerosolization of bottom ashes. Here, we show that combustion ashes (coal fly ash, wood bottom ash, domestic bottom ash, and coal bottom ash) nucleate ice in the immersion mode at conditions relevant to mixed-phase clouds. Hence, combustion ashes could play an important role in primary ice formation in mixed-phase clouds, especially in clouds that are formed near the emission source of these aerosol particles. In order to quantitatively assess the impact of combustion ashes on mixed-phase clouds, we propose that the atmospheric abundance of combustion ashes should be quantified since up to now they have mostly been classified together with mineral dust particles. Also, in reporting ice residue compositions, a distinction should be made between natural mineral dusts and combustion ashes in order to quantify the contribution of combustion ashes to atmospheric ice nucleation.

Umo, N. S.; Murray, B. J.; Baeza-Romero, M. T.; Jones, J. M.; Lea-Langton, A. R.; Malkin, T. L.; O'Sullivan, D.; Plane, J. M. C.; Williams, A.

2014-11-01

26

Theoretical study of vapor-liquid homogeneous nucleation using stability analysis of a macroscopic phase.  

PubMed

Stability analysis is generally used to verify that the solution to phase equilibrium calculations corresponds to a stable state (minimum of the free energy). In this work, tangent plane distance analysis for stability of macroscopic mixtures is also used for analyzing the nucleation process, reconciling thus this analysis with classical nucleation theories. In the context of the revised nucleation theory, the driving force and the nucleation work are expressed as a function of the Lagrange multiplier corresponding to the mole fraction constraint from the minimization problem of stability analysis. Using a van der Waals fluid applied to a ternary mixture, Lagrange multiplier properties are illustrated. In particular, it is shown how the Lagrange multiplier value is equal to one on the binodal and spinodal curves at the same time as the driving force of nucleation vanishes on these curves. Finally, it is shown that, on the spinodal curve, the nucleation work from the revised and generalized nucleation theories are characterized by two different local minima from stability analysis, irrespective of any interfacial tension models. PMID:23061836

Carreón-Calderón, Bernardo

2012-10-14

27

Two-step nucleation mechanism in solid-solid phase transitions.  

PubMed

The microscopic kinetics of ubiquitous solid-solid phase transitions remain poorly understood. Here, by using single-particle-resolution video microscopy of colloidal films of diameter-tunable microspheres, we show that transitions between square and triangular lattices occur via a two-step diffusive nucleation pathway involving liquid nuclei. The nucleation pathway is favoured over the direct one-step nucleation because the energy of the solid/liquid interface is lower than that between solid phases. We also observed that nucleation precursors are particle-swapping loops rather than newly generated structural defects, and that coherent and incoherent facets of the evolving nuclei exhibit different energies and growth rates that can markedly alter the nucleation kinetics. Our findings suggest that an intermediate liquid should exist in the nucleation processes of solid-solid transitions of most metals and alloys, and provide guidance for better control of the kinetics of the transition and for future refinements of solid-solid transition theory. PMID:25218059

Peng, Yi; Wang, Feng; Wang, Ziren; Alsayed, Ahmed M; Zhang, Zexin; Yodh, Arjun G; Han, Yilong

2015-01-01

28

Two-step nucleation mechanism in solid–solid phase transitions  

NASA Astrophysics Data System (ADS)

The microscopic kinetics of ubiquitous solid–solid phase transitions remain poorly understood. Here, by using single-particle-resolution video microscopy of colloidal films of diameter-tunable microspheres, we show that transitions between square and triangular lattices occur via a two-step diffusive nucleation pathway involving liquid nuclei. The nucleation pathway is favoured over the direct one-step nucleation because the energy of the solid/liquid interface is lower than that between solid phases. We also observed that nucleation precursors are particle-swapping loops rather than newly generated structural defects, and that coherent and incoherent facets of the evolving nuclei exhibit different energies and growth rates that can markedly alter the nucleation kinetics. Our findings suggest that an intermediate liquid should exist in the nucleation processes of solid–solid transitions of most metals and alloys, and provide guidance for better control of the kinetics of the transition and for future refinements of solid–solid transition theory.

Peng, Yi; Wang, Feng; Wang, Ziren; Alsayed, Ahmed M.; Zhang, Zexin; Yodh, Arjun G.; Han, Yilong

2015-01-01

29

Ice Nucleation in Mixed-Phase Clouds: Parameterization Evaluation and Climate Impacts  

NASA Astrophysics Data System (ADS)

There are still large uncertainties on ice nucleation mechanisms and ice crystal numbers in mixed-phase clouds, which affects modeled cloud phase, cloud lifetime and radiative properties in the Arctic clouds in global climate models. In this study we evaluate model simulations with three mixed-phase ice nucleation parameterizations (Phillips et al., 2008; DeMott et al., 2009; Meyers et al. 1992) against the Atmospheric Radiation Measurement (ARM) Indirect and Semi-Direct Aerosol Campaign (ISDAC) observations using the NCAR Community Atmospheric Model Version 4 (CAM4) running in the single column mode (SCAM) and in the CCPP-ARM Parameterization Testbed (CAPT) forecasts. It is found that SCAM and CAPT with the new physically-based ice nucleation schemes (Phillips et al., 2008; DeMott et al., 2009) produce a more realistic simulation of the cloud phase structure and the partitioning of condensed water into liquid droplets against observations during the ISDAC than the CAM with an oversimplified Meyers et al. (1992). Both SCAM simulations and CAPT forecasts suggest that the ice number concentration could play an important role in the simulated mixed-phase cloud microphysics, and thereby needs to be realistically represented in global climate models. The global climate implication of different ice nucleation parameterizations are also be studied.

Liu, X.; Ghan, S. J.; Xie, S.; Boyle, J. S.; Klein, S. A.; Demott, P. J.; Prenni, A. J.

2009-12-01

30

Quantized hard-x-ray phase vortices nucleated by aberrated nanolenses  

SciTech Connect

Quantized x-ray phase vortices, namely, screw-type topological defects in the wave fronts of a coherent monochromatic scalar x-ray wave field, may be spontaneously nucleated by x-ray lenses. Phase retrieval is used to reconstruct the phase and amplitude of the complex disturbance created by aberrated gold nanolenses illuminated with hard x rays. A nanoscale quantized x-ray vortex-antivortex dipole is observed, manifest both as a pair of opposite-helicity branch points in the Riemann sheets of the multivalued x-ray phase map of the complex x-ray field and in the vorticity of the associated Poynting vector field.

Pavlov, Konstantin M. [School of Science and Technology, University of New England, Armidale, New South Wales 2351 (Australia); School of Physics, Monash University, Victoria 3800 (Australia); Paganin, David M. [School of Physics, Monash University, Victoria 3800 (Australia); Vine, David J. [ARC Centre of Excellence for Coherent X-ray Science, School of Physics, The University of Melbourne, Parkville, Victoria 3010 (Australia); Schmalz, Jelena A. [School of Science and Technology, University of New England, Armidale, New South Wales 2351 (Australia); Suzuki, Yoshio; Uesugi, Kentaro; Takeuchi, Akihisa; Yagi, Naoto [SPring-8/JASRI (Japan Synchrotron Radiation Research Institute), Hyogo 679-5198 (Japan); Kharchenko, Alexander; Blaj, Gabriel [PANalytical B.V., P.O. Box 13, 7600 AA Almelo (Netherlands); Jakubek, Jan [Institute of Experimental and Applied Physics, Czech Technical University in Prague, 166 36 Prague 6 (Czech Republic); Altissimo, Matteo [Melbourne Centre for Nanofabrication, 151 Wellington Road, Clayton, Victoria 3168 (Australia); Materials Science and Engineering, Commonwealth Scientific and Industrial Research Organisation, Clayton South, Victoria 3169 (Australia); Clark, Jesse N. [London Centre for Nanotechnology, University College, Gower St, London WC1E 6BT (United Kingdom)

2011-01-15

31

Numerical Analysis of Bubble Nucleation Processes for First-Order Phase Transitions Within Quantum Fields  

NASA Astrophysics Data System (ADS)

The well established links between statistical mechanics and quantum field theory have resulted in the extension of the theory of phase transitions to quantum fields. Within this framework first-order phase transition rates for quantum fields have traditionally been calculated via the Coleman "thin-wall" approximation. This approximation scheme is claimed to have validity in the situation where a first-order phase transition takes place between two nearly degenerate vacuum (ground) states. It is the purpose of this dissertation to make a comprehensive study of the range of validity of the "thin -wall" approximation via a comparison of its results with exact results obtained numerically. It is found that both in the absence of gravity and the presence of gravity the "thin-wall" approximation has a very restricted range of validity, and that it characteristically overestimates the phase transition rate. A new approximation scheme is presented which considerably improves upon the original "thin-wall" approximation, yet requires roughly the same degree of calculation effort as the original "thin-wall" approximation. The numerical analysis of first-order phase transitions within quantum fields is also extended to regimes not applicable to the "thin-wall" approximation in a search for new physical effects. An evolution from the "thin-wall" tunneling mode to the Hawking-Moss tunneling mode is observed for the decay from a de Sitter spacetime to a Minkowski spacetime. For the decay from Minkowski spacetime to an anti-de Sitter spacetime, the "thin-wall" approximation is seen to over -estimate the size of the "forbidden region" (predicted within the "thin-wall" approximation) in which the transition is not allowed. The effect of gravitationally compact objects upon vacuum phase transitions is considered within a perturbative analysis. It is found that they may act as nucleation sites for first-order phase transitions. The nucleation rate is maximized when the size of the gravitationally compact object is comparable to the size of the nucleating bubble associated with the phase transition. Some astrophysical applications of first-order vacuum phase transitions are analyzed. In particular, the post-nucleation evolution of a bubble of "new" phase; together with a relationship between the number density of possible astrophysical nucleation sites within the Universe (e.g., microscopic black-holes) and the mass of fermions within the Standard Model.

Samuel, David Adrian

32

Gas-phase chemical dynamics  

SciTech Connect

Research in this program is directed towards the spectroscopy of small free radicals and reactive molecules and the state-to-state dynamics of gas phase collision, energy transfer, and photodissociation phenomena. Work on several systems is summarized here.

Weston, R.E. Jr.; Sears, T.J.; Preses, J.M. [Brookhaven National Laboratory, Upton, NY (United States)

1993-12-01

33

Gas phase catalysis by zeolites  

Microsoft Academic Search

This paper provides an overview about today’s use of zeolites and related microporous materials as catalysts within the fields of refining, petrochemistry and commodity chemicals. The content of this presentation is devoted to gas phase catalysis—with focus on acid catalysis, hydrocarbon conversion and formation, oil and natural gas upgrading as well as catalytic probe reactions for the characterisation of zeolites

Michael Stöcker

2005-01-01

34

Quantification of gypsum crystal nucleation, growth, and breakage rates in a wet flue gas desulfurization pilot plant  

Microsoft Academic Search

The aim of this work is to study the influence of nucleation, growth and breakage on the particle size distribution (PSD) of gypsum crystals produced by the wet flue gas desulfurization (FGD) process. The steady state PSD, obtained in a falling film wet FGD pilot plant during desulfurization of a 1000 ppm(V) SO gas stream, displayed a strong nonlinear behaviour

Brian B. Hansen; Søren Kiil; Jan E. Johnsson

2009-01-01

35

Phase separation in solid 3He-4He mixtures: Comparison with theory of homogeneous nucleation  

NASA Astrophysics Data System (ADS)

NMR and pressure have been measured in a solid 3He-4He mixture as the temperature was lowered in steps through phase separation. The spin-echo method was used to detect the behavior typical for bounded diffusion and to estimate the diffusion coefficient, size and cluster concentration in the 3He-enriched phase. The characteristic phase separation time constant of the mixture was found to decrease at lower temperatures. The results convincingly support homogeneous nucleation. From a comparison with theory, the surface tension at the boundary of the phase-separated clusters is found either from the cluster concentration, determined by NMR, or from the separation time constant, determined by pressure measurements. The results of the two independent determinations agree well and yield a surface tension coefficient of 1.27×10-2 erg/cm2 (1.27×10-5 J/m2).

Smith, A.; Maidanov, V. A.; Rudavskii, E. Ya.; Grigor'ev, V. N.; Slezov, V. V.; Poole, M.; Saunders, J.; Cowan, B.

2003-06-01

36

Surface area controlled heterogeneous nucleation.  

PubMed

Heterogeneous nucleation of liquid from a gas phase on nanoparticles has been studied under various saturation ratios and nuclei size. The probability of liquid droplet nucleation, especially at a low degree of deviation from equilibrium, was measured for both atmospheric aerosol particles and engineered nanoparticles Cr(2)O(3). The concept of a critical saturation ratio and the validity of the one-to-one relationship between the nuclei number and the number of droplets were examined. A transient zone between no nucleation and established nucleation termed the surface area controlled nucleation was observed. In this zone, the probability of stable phase formation is determined by the surface area of nuclei. There are two distinctive features of the surface area controlled nucleation: the nucleation probability is much less than 1 and is proportional to the surface area of nuclei. For condensation particle counters (CPCs) counting nanoparticles, these features mean that counts measured are proportional to the surface area of nanoparticles and, therefore, the CPCs counts can be calibrated to measure the surface area. PMID:22320756

Steer, Brian; Gorbunov, Boris; Rowles, Jonathan; Green, David

2012-02-01

37

Gas phase atmospheric bromine photochemistry  

Microsoft Academic Search

This paper reviews the current knowledge of gas phase bromine photochemistry and presents a budget study of atmospheric bromine species. The effectiveness of the ozone catalytic loss cycles involving bromine is quantified by considering their chain length and effectiveness. The chain effectiveness is a new variable defined as the chain length multiplied by the rate of the cycle's rate-limiting step.

D. J. Lary

1996-01-01

38

Characterization of early stage intermediates in the nucleation phase of A? aggregation.  

PubMed

Alzheimer's disease (AD) is a common form of dementia, which is characterized by the presence of extracellular amyloid plaques comprising the amyloid ? peptide (A?). Although the mechanism underlying AD pathogenesis remains elusive, accumulating evidence suggests that the process of amyloid fibril formation is a surface-mediated event, which plays an important role in AD onset and progression. In this study, the mechanism of A? aggregation on hydrophobic surfaces was investigated with dual polarization interferometry (DPI), which provides real-time information on early stages of the aggregation process. Aggregation was monitored on a hydrophobic C18 surface and a polar silicon oxynitride surface. The DPI results showed a characteristic A? aggregation pattern involving a decrease in the density of A? at the surface followed by an increase in the thickness on the hydrophobic C18 chip. Most importantly, the DPI measurements provided unique information on the early stages of A? aggregation, which is characterized by the presence of initially slow nucleus formation process followed by exponential fibril elongation. The dimensions of the putative nucleus corresponded to a thickness of ?5 nm for both A?40 and A?42, which may represent about 10-15 molecules. The results thus support the nucleation-dependent polymerization model as indicated by the presence of a nucleation phase followed by an exponential growth phase. These results are the first reported measurements of the real-time changes in A? molecular structure during the early stages of amyloid formation at the nanometer level. PMID:22283417

Zhai, Jiali; Lee, Tzong-Hsien; Small, David H; Aguilar, Marie-Isabel

2012-02-14

39

Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystals and Polytetrahedral-Phase-Forming Alloys  

NASA Technical Reports Server (NTRS)

The local atomic structures of undercooled liquid metals are presumed to be icosahedral; this order is incompatible with translational periodicity, constituting a barrier to the nucleation of the crystal phase. The extended atomic structure of the icosahedral quasicrystal (i-phase) is similar to that presumed in the undercooled liquid. Therefore, a comparison of the maximum undercooling in alloys that form the i-phase with those that form crystal phases provides a probe of the liquid structure.

Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rogers, J. R.; Robinson, M. B.; Rathz, T. J.; Krishnan, S.; Curreri, Peter A. (Technical Monitor)

2002-01-01

40

Thin interface analysis of a phase-field model for epitaxial growth with nucleation and Ehrlich-Schwoebel effects  

NASA Astrophysics Data System (ADS)

In this paper, we perform thin interface analysis of a quantitative phase field model for epitaxial growth where nucleation and the Ehrlich-Schwoebel barrier have been considered. Results show that once the nucleation term is introduced into the phase-field model, modification must be carried out to get rid of the extrinsic “kinetic nucleation effect”. While in the ES effect, the asymmetric diffusivity accounts for an irrational step motion that leads the model to deviate from the sharp-interface approximation, hence another modification for the attachment time should be carried. Attributed to these modifications, the phase-field model is more quantitative in describing step flow dynamics in the sharp-interface limit, as well as exhibiting the more convergence of the steady-state velocity with respect to the step width for larger scale simulations. Our analysis and modifications explore the quantitative linking between atom motions and step dynamics.

Dong, X. L.; Xing, H.; Chen, C. L.; Luo, B. C.; Chen, Z.; Zhang, R. L.; Jin, K. X.

2014-11-01

41

Microphysical consequences of the spatial distribution of ice nucleation in mixed-phase stratiform clouds  

NASA Astrophysics Data System (ADS)

Mixed-phase stratiform clouds can persist even with steady ice precipitation fluxes, and the origin and microphysical properties of the ice crystals are of interest. Vapor deposition growth and sedimentation of ice particles along with a uniform volume source of ice nucleation lead to a power law relation between ice water content wi and ice number concentration ni with exponent 2.5. The result is independent of assumptions about the vertical velocity structure of the cloud and is therefore more general than the related expression of Yang et al. (2013). The sensitivity of the wi-ni relationship to the spatial distribution of ice nucleation is confirmed by Lagrangian tracking and ice growth with cloud volume, cloud top, and cloud base sources of ice particles through a time-dependent cloud field. Based on observed wi and ni from Indirect and Semi-Direct Aerosol Campaign, a lower bound of 0.006 m-3 s-1 is obtained for the ice crystal formation rate.

Yang, Fan; Ovchinnikov, Mikhail; Shaw, Raymond A.

2014-07-01

42

Cluster Nucleation and Growth from a Highly Supersaturated Adatom Phase: Silver on Magnetite  

PubMed Central

The atomic-scale mechanisms underlying the growth of Ag on the (?2×?2)R45°-Fe3O4(001) surface were studied using scanning tunneling microscopy and density functional theory based calculations. For coverages up to 0.5 ML, Ag adatoms populate the surface exclusively; agglomeration into nanoparticles occurs only with the lifting of the reconstruction at 720 K. Above 0.5 ML, Ag clusters nucleate spontaneously and grow at the expense of the surrounding material with mild annealing. This unusual behavior results from a kinetic barrier associated with the (?2×?2)R45° reconstruction, which prevents adatoms from transitioning to the thermodynamically favorable 3D phase. The barrier is identified as the large separation between stable adsorption sites, which prevents homogeneous cluster nucleation and the instability of the Ag dimer against decay to two adatoms. Since the system is dominated by kinetics as long as the (?2×?2)R45° reconstruction exists, the growth is not well described by the traditional growth modes. It can be understood, however, as the result of supersaturation within an adsorption template system. PMID:24945923

2014-01-01

43

Morphology of gel phase domains produced by random nucleation in supported lipid membranes  

NASA Astrophysics Data System (ADS)

We explored the morphology and dynamics of domain growth resulting from lateral phase separation in phospholipid membranes. Planar supported films composed of mixtures of distearoylethyl-phosphatidylcholine (DSEPC)/dimyristoylphosphatidylcholine (DMPC) and distearoylphosphatidylcholine (DSPC)/dimyristoylphosphatidylcholine (DMPC) have been imaged in fluid using temperature- and time-dependent atomic force microscopy (AFM). We find that the lipid domains length scale is in the micrometer range for multilayers (bilayer deposited on top of another bilayer) of DSEPC/DMPC and bilayers of DSPC/DMPC but in nanometer range for a single supported bilayer of DSEPC/DMPC. Fluorescence Recovery After Photobleaching indicate that the diffusion in the fluid phase is much lower for the supported DSEPC/DMPC bilayers than for the supported DSPC/DMPC bilayers and that the decrease is due to the fact that the DSEPC chains interdigitate. When the diffusion is slowed the growth is due mainly to random nucleation and not by diffusive transport. Our results suggest that by choosing the growth mechanism of the gel phase domains in a supported lipid bilayer one can control the size and morphology of the phase separated domains.

Muresan, Adrian; Lee, Ka Yee

2003-03-01

44

Ion-induced nucleation in polar one-component fluids  

E-print Network

We present a Ginzburg-Landau theory of ion-induced nucleation in a gas phase of polar one-component fluids, where a liquid droplet grows with an ion at its center. By calculating the density profile around an ion, we show that the solvation free energy is larger in gas than in liquid at the same temperature on the coexistence curve. This difference much reduces the nucleation barrier in a metastable gas.

Hikaru Kitamura; Akira Onuki

2005-08-01

45

Investigating relationships between the seismic "nucleation" phases and breakaway phases of recent Mw 8 earthquakes using global broadband seismic observations  

NASA Astrophysics Data System (ADS)

It is known that the far field P wave velocity observations of large earthquakes frequently start with a small interval of weak motion, which was described as "fore-shock", "pre-shock", or seismic nucleation phase (SNP) by various researchers, e.g, Ellsworth and Beroza (1995). The energetic ground motion immediately following this interesting phase was named as "breakaway" phase. Recent global surveys indicate that for about 50% of Mw>7.5 earthquakes their SNP could be observed teleseismically and the distribution of the earthquakes with SNP appears to be correlated with the tectonic environment and focal mechanisms (Ji et al, 2010; Burkhart and Ji, 2011). Here, a multiple double-couple (MDC) algorithm is developed to quantitatively investigate the relationship between the SNPs and "breakaway" phases of 22 Mw>8 earthquakes since 1990. Our preliminary analysis indicates that the average moment acceleration during the first 4 s of the 2011 Mw 9.1 Tohoku earthquake is only about 2% of that associating with subsequent "breakaway" rupture stage. As the rupture of moderate or large earthquakes often initiate at the vicinity of one of their high slip fault patches, i.e., asperities (Mai et al., 2005), this kind of big discrepancies might shed the light on the intrinsic differences between the asperity and the weak zone in its vicinity, as hypothesized by the asperity theory (e.g., Kanamori, 1981).

Ji, C.

2012-12-01

46

The dominance of nucleation: The Jewish experience in the early phase of Jewish settlement  

Microsoft Academic Search

The dominance of the nucleated pattern among Jewish settlement in Palestine is not merely the outcome of central planning. The early colonies, established between 1882 and 1914, were already nucleated, although there was some experimentation with other patterns. The main type of settlement established in this period, with which the present study deals, was themoshava. This freeholder family-farm village was

Yossi Katz; David Grossman

1993-01-01

47

Transient nucleation in glasses  

NASA Technical Reports Server (NTRS)

Nucleation rates in condensed systems are frequently not at their steady state values. Such time dependent (or transient) nucleation is most clearly observed in devitrification studies of metallic and silicate glasses. The origin of transient nucleation and its role in the formation and stability of desired phases and microstructures are discussed. Numerical models of nucleation in isothermal and nonisothermal situations, based on the coupled differential equations describing cluster evolution within the classical theory, are presented. The importance of transient nucleation in glass formation and crystallization is discussed.

Kelton, K. F.

1991-01-01

48

Order and phase nucleation in non-equilibrium nanocomposite Fe-Pt thin films with perpendicular magnetic anisotropy.  

SciTech Connect

We report on the time evolution of mass transport upon annealing nonequilibrium Fe-Pt nanocomposite films, leading to nucleation of L1{sub 0} chemically ordered phase. The nonequilibrium nanocomposite films were fabricated by applying Fe{sup +} ion implantation to epitaxial Pt films grown on (001) MgO substrates, yielding Fe nanoclusters embedded in a Pt matrix at a tailored penetration depth. Time-resolved x-ray diffraction studies were carried out using synchrotron radiation, allowing determination of the activation energy for nucleation of the FePt L1{sub 0} phase within the segregated nanoclusters during annealing. The growth of the segregated L1{sub 0} ordered phase was modeled using ideal grain-size law and found to be dominated by strain-driven surface nucleation. The activation energies were found to correlate with the nanocluster size. Magnetic characterization of selected annealed samples indicates perpendicular magnetic anisotropy with high coercive field coincident with high value of the chemical order parameter of the ordered phase within the magnetic nanoclusters.

Clavero, C.; Skuza, J. R.; Garcia-Martin, J. M.; Cebollada, A.; Walko, D. A.; Lukaszew, R. A.; Coll. of William and Mary; Inst. de Microelectronica de Madrid

2009-03-01

49

Influence of ferrite nanoparticle type and content on the crystallization kinetics and electroactive phase nucleation of poly(vinylidene fluoride).  

PubMed

This work reports on the nucleation of the ?-phase of poly(vinylidene fluoride) (PVDF) by incorporating CoFe(2)O(4) and NiFe(2)O(4) nanoparticles, leading in this way to the preparation of magnetoelectric composites. The fraction of filler nanoparticles needed to produce the same ?- to ?-phase ratio in crystallized PVDF is 1 order of magnitude lower in the cobalt ferrite nanoparticles. The interaction between nanoparticles and PVDF chains induce the all-trans conformation in PVDF segments, and this structure then propagates in crystal growth. The nucleation kinetics is enhanced by the presence of nanoparticles, as corroborated by the increasing number of spherulites with increasing nanoparticle content and by the variations of the Avrami's exponent. Further, the decrease of the crystalline fraction of PVDF with increasing nanoparticle content indicates that an important fraction of polymer chains are confined in interphases with the filler particle. PMID:21545124

Sencadas, Vitor; Martins, Pedro; Pitães, Alexandre; Benelmekki, Maria; Gómez Ribelles, José Luis; Lanceros-Mendez, Senentxu

2011-06-01

50

Effects of the cosmological expansion on the bubble nucleation rate for relativistic first-order phase transitions  

NASA Astrophysics Data System (ADS)

I calculate the first corrections to the dynamical preexponential factor of the bubble nucleation rate for a relativistic first-order phase transition in an expanding cosmological background by estimating the effects of the Hubble expansion rate on the critical bubbles of Langer’s statistical theory of metastability. I also comment on possible applications and problems that arise when one considers the field theoretical extensions of these results (the Coleman De Luccia and Hawking-Moss instantons and decay rates).

Metaxas, Dimitrios

2008-09-01

51

Inclusion phases and the nucleation of acicular ferrite in submerged arc welds in high strength low alloy steels  

Microsoft Academic Search

Series of submerged arc welds of HSLA steel made with three different fluxes and metallic additions of Ti, Mo, and Cr have\\u000a been examined to study the inclusions and their role in the nucleation of acicular ferrite. Inclusion phases and compositions\\u000a have been analyzed by electron diffraction and X-ray microanalysis. These analyses have shown that the inclusions contained\\u000a many different

J. M. Dowling; J. M. Corbett; H. W. Kerr

1986-01-01

52

Phase field theory of interfaces and crystal nucleation in a eutectic system of fcc structure: I. Transitions in the one-phase liquid region  

NASA Astrophysics Data System (ADS)

The phase field theory (PFT) has been applied to predict equilibrium interfacial properties and nucleation barrier in the binary eutectic system Ag-Cu using double well and interpolation functions deduced from a Ginzburg-Landau expansion that considers fcc (face centered cubic) crystal symmetries. The temperature and composition dependent free energies of the liquid and solid phases are taken from CALculation of PHAse Diagrams-type calculations. The model parameters of PFT are fixed so as to recover an interface thickness of ˜1nm from molecular dynamics simulations and the interfacial free energies from the experimental dihedral angles available for the pure components. A nontrivial temperature and composition dependence for the equilibrium interfacial free energy is observed. Mapping the possible nucleation pathways, we find that the Ag and Cu rich critical fluctuations compete against each other in the neighborhood of the eutectic composition. The Tolman length is positive and shows a maximum as a function of undercooling. The PFT predictions for the critical undercooling are found to be consistent with experimental results. These results support the view that heterogeneous nucleation took place in the undercooling experiments available at present. We also present calculations using the classical droplet model [classical nucleation theory (CNT)] and a phenomenological diffuse interface theory (DIT). While the predictions of the CNT with a purely entropic interfacial free energy underestimate the critical undercooling, the DIT results appear to be in a reasonable agreement with the PFT predictions.

Tóth, Gyula I.; Gránásy, László

2007-08-01

53

Gas temperature effect on the time for onset of particle nucleation in argon diluted acetylene plasma  

E-print Network

, Serbia and Montenegro 1. Introduction Particle nucleation in processing plasmas is an important issue to understand the basic problems of the involved plasma chemistry. On the other hand it is interesting plasma I. Stefanovi1, 2 , E. Kovacevi1 , J. Berndt1 , and J. Winter1 1 Institute for Experimental Physics

Paris-Sud XI, Université de

54

Effects of strain on phonon interactions and phase nucleation in several semiconductor and nano particle systems  

NASA Astrophysics Data System (ADS)

Raman scattering is utilized to explore the effects of applied pressure and strain on anharmonic phonon interactions and nucleation of structural transitions in several bulk and nanoparticle semiconductor systems. The systems investigated are bulk ZnS and ZnSe in several isotopic compositions, InP/CdS core/shell nanoparticles exhibiting confined and surface optical Raman modes, and amorphous selenium films undergoing photo-induced crystallization. The anharmonic decay of long-wavelength optical modes into two-phonon acoustic combinations modes is studied in 64Zn32S, 64Zn34S, natZnatS bulk crystals by measuring the TO(Gamma) Raman line-shape as a function of applied hydrostatic pressure. The experiments are carried out at room temperature and 16K for pressures up to 150 kbars using diamond-anvil cells. The most striking effects occur in 68Zn32S where the TO(Gamma) peak narrows by a factor of 10 and increases in intensity at pressures for which the TO(Gamma) frequency has been tuned into a gap in the two-phonon density of states (DOS). In all the isotopic compositions, the observed phonon decay processes can be adequately explained by a second order perturbation treatment of the anharmonic coupling between TO(Gamma) and TA + LA combinations at various critical points, combined with an adiabatic bond-charge model for the phonon DOS and the known mode Gruneisen parameters. Bulk ZnSe crystals exhibit very different behavior. Here we find that anharmonic decay alone can not explain the excessive (˜ 60 cm-1 ) broadening in the TO(Gamma) Raman peak observed as the pressure approaches to within 50kbar of the ZB -> B1 phase transition (at P ˜ 137 kbar). Rather the broadening appears to arise from antecedent nucleation of structural changes within nanoscopic domains, with the mechanism for line-shape changes being mode mixing via localization and disorder instead of anharmonicity. To sort out these contributions, pressure experiments on natural ZnSe and on isotopically pure 68Zn76Se are compared. Again we use an appropriate bond-charge model to obtain the phonon DOS. It is concluded that the antecedent nucleation mechanism is much more important in ZnSe than in ZnS. In order to further investigate interactions of vibrational modes in spatially confined systems, pressure-Raman experiments are carried out on InP/CdS core/shell nanoparticles. This system differs from most other core/shell nanoparticles systems, in that the near degeneracy of the bulk InP TO(Gamma) and CdS LO(Gamma) phonons leads to possible cross-interface mode coupling. Different confined and surface (or interface) optical modes are studied as a function of pressure up 65 kbar at 373 and 230 K. The results are compared with the predictions of dielectric continuum theory using a phenomenological macroscopic approach (PMA) to include the pressure dependence. Three different pressure media are employed, and the effects on the surface modes of their different static dielectric constants are investigated. The pressure-shifts of the observed confined and surface modes are well accounted for without the need to include cross-interface coupling. We conclude that the conventional boundary condition, of vanishing phonon amplitude at the heterointerface, remains valid in the InP/CdS nanoparticle system, in spite of the near degeneracy of the bulk optical phonons. Photo-induced crystallization in amorphous selenium (a-Se) was also explored in this dissertation, as another example of a nanoscopic nucleation process influenced by strain, in this case internal strain. In order to observe photo-crystallization, the Raman spectra of commercial a-Se films used as targets in high-gain avalanche rushing photodetectors (HARP) cameras was studied at temperatures in the range 260 - 330 K. We find a rich temperature behavior that reflects the competition of changes in viscosity and strain, and defines four distinct regimes. These results are in qualitative accord with a theory by R.B.Stephens treating the effects of local strain on the secondary growth of crystalline nuclei in a-Se. W

Tallman, Robert E.

55

Phase field models for heterogeneous nucleation: Application to inoculation in alpha-solidifying Ti-Al-B alloys  

NASA Astrophysics Data System (ADS)

This paper aims at briefly reviewing phase field models applied to the simulation of heterogeneous nucleation and subsequent growth, with special emphasis on grain refinement by inoculation. The spherical cap and free growth model (e.g. A.L. Greer, et al., Acta Mater. 48, 2823 (2000)) has proven its applicability for different metallic systems, e.g. Al or Mg based alloys, by computing the grain refinement effect achieved by inoculation of the melt with inert seeding particles. However, recent experiments with peritectic Ti-Al-B alloys revealed that the grain refinement by TiB2 is less effective than predicted by the model. Phase field simulations can be applied to validate the approximations of the spherical cap and free growth model, e.g. by computing explicitly the latent heat release associated with different nucleation and growth scenarios. Here, simulation results for point-shaped nucleation, as well as for partially and completely wetted plate-like seed particles will be discussed with respect to recalescence and impact on grain refinement. It will be shown that particularly for large seeding particles (up to 30 ?m), the free growth morphology clearly deviates from the assumed spherical cap and the initial growth - until the free growth barrier is reached - significantly contributes to the latent heat release and determines the recalescence temperature.

Apel, M.; Eiken, J.; Hecht, U.

2014-02-01

56

Finite-size effects on liquid-solid phase coexistence and the estimation of crystal nucleation barriers.  

PubMed

A fluid in equilibrium in a finite volume V with particle number N at a density ?=N/V exceeding the onset density ?_{f} of freezing may exhibit phase coexistence between a crystalline nucleus and surrounding fluid. Using a method suitable for the estimation of the chemical potential of dense fluids, we obtain the excess free energy due to the surface of the crystalline nucleus. There is neither a need to precisely locate the interface nor to compute the (anisotropic) interfacial tension. As a test case, a soft version of the Asakura-Oosawa model for colloid-polymer mixtures is treated. While our analysis is appropriate for crystal nuclei of arbitrary shape, we find the nucleation barrier to be compatible with a spherical shape and consistent with classical nucleation theory. PMID:25635552

Statt, Antonia; Virnau, Peter; Binder, Kurt

2015-01-16

57

Finite-Size Effects on Liquid-Solid Phase Coexistence and the Estimation of Crystal Nucleation Barriers  

NASA Astrophysics Data System (ADS)

A fluid in equilibrium in a finite volume V with particle number N at a density ? =N /V exceeding the onset density ?f of freezing may exhibit phase coexistence between a crystalline nucleus and surrounding fluid. Using a method suitable for the estimation of the chemical potential of dense fluids, we obtain the excess free energy due to the surface of the crystalline nucleus. There is neither a need to precisely locate the interface nor to compute the (anisotropic) interfacial tension. As a test case, a soft version of the Asakura-Oosawa model for colloid-polymer mixtures is treated. While our analysis is appropriate for crystal nuclei of arbitrary shape, we find the nucleation barrier to be compatible with a spherical shape and consistent with classical nucleation theory.

Statt, Antonia; Virnau, Peter; Binder, Kurt

2015-01-01

58

Quantification of gypsum crystal nucleation, growth, and breakage rates in a wet flue gas desulfurization pilot plant  

SciTech Connect

The aim of this work is to study the influence of nucleation, growth and breakage on the particle size distribution (PSD) of gypsum crystals produced by the wet flue gas desulfurization (FGD) process. The steady state PSD, obtained in a falling film wet FGD pilot plant during desulfurization of a 1000 ppm(V) SO{sub 2} gas stream, displayed a strong nonlinear behaviour (in a ln(n(l)) vs. I plot) at the lower end of the particle size range, compared to the well-known linear mixed suspension mixed product removal model. A transient population balance breakage model, fitted to experimental data, was able to model an increase in the fraction of small particles, but not to the extent observed experimentally. A three-parameter, size-dependent growth model, previously used for sodium sulphate decahydrate and potash alum, was able to describe the experimental data, indicating either size-dependent integration kinetics or growth rate dispersion.

Hansen, B.B.; Kiil, S.; Johnsson, J.E. [Technical University of Denmark, Lyngby (Denmark). Dept. of Chemical & Biochemical Engineering

2009-10-15

59

Homogeneous vs. heterogeneous nucleation in water-dicarboxylic acid systems  

NASA Astrophysics Data System (ADS)

Binary heterogeneous nucleation of water-succinic/glutaric/malonic/adipic acid on nanometer-sized particles is investigated within the frame of classical heterogeneous nucleation theory. Homogeneous nucleation is also included for comparison. It is found that the nucleation probabilities depend on the contact angle and on the size of the seed particles. New thermodynamical properties, such as saturation vapor pressure, density and surface tension for all the dicarboxylic acid aqueous solutions are included in the calculations. While the new surface tension and density formulations do not bring any significant difference in the computed nucleation rate for homogeneous nucleation for succinic and glutaric acids, the use of the newly derived equations for the vapor pressure decrease the acid concentrations in gas phase with 3 orders of magnitude. According to our calculations, the binary heterogeneous nucleation of succinic acid-water and glutaric acid-water although it requires a 3 4 orders of magnitude lower vapor concentrations than the homogeneous nucleation cannot take place in atmospheric conditions. On the other hand binary homogeneous nucleation of adipic acid-water systems might be possible in conditions occuring in upper boundary layer. However, a more detailed characterization of the interaction between the surface and the molecules of the nucleating vapor should be considered in the future.

Hienola, A. I.; Vehkamäki, H.; Riipinen, I.; Kulmala, M.

2008-10-01

60

Homogeneous vs. heterogeneous nucleation in water-dicarboxylic acid systems  

NASA Astrophysics Data System (ADS)

Binary heterogeneous nucleation of water-succinic/glutaric/malonic/adipic acid on nanometer-sized particles is investigated within the frame of classical heterogeneous nucleation theory. Homogeneous nucleation is also included for comparison. It is found that the nucleation probabilities depend on the contact angle and on the size of the seed particles. New thermodynamical properties, such as saturation vapor pressure, density and surface tension for all the dicarboxylic acid aqueous solutions are included in the calculations. While the new surface tension and density formulations do not bring any significant difference in the computed nucleation rate for homogeneous nucleation for succinic and glutaric acids, the use of the newly derived equations for the vapor pressure decrease the acid concentrations in gas phase by 3 orders of magnitude. According to our calculations, the binary heterogeneous nucleation of succinic acid-water and glutaric acid-water - although it requires a 3-4 orders of magnitude lower vapor concentrations than the homogeneous nucleation - cannot take place under atmospheric conditions. On the other hand binary homogeneous nucleation of adipic acid-water systems might be possible under conditions occuring in upper boundary layer. However, a more detailed characterization of the interaction between the surface and the molecules of the nucleating vapor should be considered in the future.

Hienola, A. I.; Vehkamäki, H.; Riipinen, I.; Kulmala, M.

2009-03-01

61

Gas-Phase Infrared; JCAMP Format  

National Institute of Standards and Technology Data Gateway

SRD 35 NIST/EPA Gas-Phase Infrared; JCAMP Format (PC database for purchase)   This data collection contains 5,228 infrared spectra in the JCAMP-DX (Joint Committee for Atomic and Molecular Physical Data "Data Exchange") format.

62

Project ARGO: Gas phase formation in simulated microgravity  

NASA Technical Reports Server (NTRS)

The ARGO study investigated the reduced incidence of joint pain decompression sickness (DCS) encountered in microgravity as compared with an expected incidence of joint pain DCS experienced by test subjects in Earth-based laboratories (unit gravity) with similar protocols. Individuals who are decompressed from saturated conditions usually acquire joint pain DCS in the lower extremities. Our hypothesis is that the incidence of joint pain DCS can be limited by a significant reduction in the tissue gas micronuclei formed by stress-assisted nucleation. Reductions in dynamic and kinetic stresses in vivo are linked to hypokinetic and adynamic conditions of individuals in zero g. We employed the Doppler ultrasound bubble detection technique in simulated microgravity studies to determine quantitatively the degree of gas phase formation in the upper and lower extremities of test subjects during decompression. We found no evidence of right-to-left shunting through pulmonary vasculature. The volume of gas bubble following decompression was examined and compared with the number following saline contrast injection. From this, we predict a reduced incidence of DCS on orbit, although the incidence of predicted mild DCS still remains larger than that encountered on orbit.

Powell, Michael R.; Waligora, James M.; Norfleet, William T.; Kumar, K. Vasantha

1993-01-01

63

Solubility of aqueous methane under metastable conditions: implications for gas hydrate nucleation.  

PubMed

To understand the prenucleation stage of methane hydrate formation, we measured methane solubility under metastable conditions using molecular dynamics simulations. Three factors that influence solubility are considered: temperature, pressure, and the strength of the modeled van der Waals attraction between methane and water. Moreover, the naturally formed water cages and methane clusters in the methane solutions are analyzed. We find that both lowering the temperature and increasing the pressure increase methane solubility, but lowering the temperature is more effective than increasing the pressure in promoting hydrate nucleation because the former induces more water cages to form while the latter makes them less prevalent. With an increase in methane solubility, the chance of forming large methane clusters increases, with the distribution of cluster sizes being exponential. The critical solubility, beyond which the metastable solutions spontaneously form hydrate, is estimated to be ~0.05 mole fraction in this work, corresponding to the concentration of 1.7 methane molecules/nm(3). This value agrees well with the cage adsorption hypothesis of hydrate nucleation. PMID:23639139

Guo, Guang-Jun; Rodger, P Mark

2013-05-30

64

Ion-induced nucleation in polar one-component fluids Hikaru Kitamuraa  

E-print Network

Ion-induced nucleation in polar one-component fluids Hikaru Kitamuraa and Akira Onuki Department; published online 27 September 2005 We present a Ginzburg-Landau theory of ion-induced nucleation in a gas phase of polar one-component fluids, where a liquid droplet grows with an ion at its center

65

GAS PHASE EXPOSURE HISTORY DERIVED FROM MATERIAL PHASE CONCENTRATION PROFILES USING SOLID PHASE MICRO-EXTRACTION  

EPA Science Inventory

EPA Identifier: F8P31059 Title: Gas Phase Exposure History Derived from Material Phase Concentration Profiles Using Solid Phase Micro-Extraction Fellow (Principal Investigator): Jonathan Lewis McKinney Institution: University of Missouri - ...

66

Nucleation Behavior of Oxygen-Acetylene Torch-Produced Diamond Films  

NASA Technical Reports Server (NTRS)

A mechanism is presented for the nucleation of diamond in the combustion flame environment. A series of six experiments and two associated simulations provide results from which the mechanism was derived. A substantial portion of the prior literature was reviewed and the data and conclusions from the previous experimenters were found to support the proposed mechanism. The nucleation mechanism builds on the work of previous researchers but presents an approach to nucleation in a detail and direction not fully presented heretofore. This work identifies the gas phase as the controlling environment for the initial formation steps leading to nucleation. The developed mechanism explains some of the difficulty which has been found in producing single crystal epitaxial films. An experiment which modified the initial gas phase precursor using methane and carbon monoxide is presented. Addition of methane into the precursor gases was found to be responsible for pillaring of the films. Atomic force microscopy surface roughness data provides a reasonable look at suppression of nucleation by carbon monoxide. Surface finish data was taken on crystals which were open to the nucleation environment and generally parallel to the substrate surface. The test surfaces were measured as an independent measure of the instantaneous nucleation environent. A gas flow and substrate experiment changed the conditions on the surface of the sample by increasing the gas flow rate while remaining on a consistent point of the atomic constituent diagram, and by changing the carbide potential of the substrate. Two tip modification experiments looked at the behavior of gas phase nucleation by modifying the shape and behavior of the flame plasma in which the diamond nucleation is suspected to occur. Diamond nucleation and growth was additionally examined using a high-velocity oxygen fuel gun and C3H6 as the fuel gas phase precursor with addition of carbon monoxide gas 01 addition of liquid toluene.

Roberts, F. E.

2003-01-01

67

Ionic liquid stationary phases for gas chromatography.  

PubMed

This article provides a summary of the development of ionic liquids as stationary phases for gas chromatography beginning with early work on packed columns that established details of the retention mechanism and established working methods to characterize selectivity differences compared with molecular stationary phases through the modern development of multi-centered cation and cross-linked ionic liquids for high-temperature applications in capillary gas chromatography. Since there are many reviews on ionic liquids dealing with all aspects of their chemical and physical properties, the emphasis in this article is placed on the role of gas chromatography played in the design of ionic liquids of low melting point, high thermal stability, high viscosity, and variable selectivity for separations. Ionic liquids provide unprecedented opportunities for extending the selectivity range and temperature-operating range of columns for gas chromatography, an area of separation science that has otherwise been almost stagnant for over a decade. PMID:21290604

Poole, Colin F; Poole, Salwa K

2011-04-01

68

Gas Accretion by Globular Clusters and Nucleated Dwarf Galaxies and the Formation of the Arches and Quintuplet Clusters  

E-print Network

We consider here the collective accretion of gas by globular clusters and dwarf galaxies moving through the interstellar medium. In the limit of high velocity and/or sound speed of the ISM, the collective potential of the cluster is insufficient to accrete significant amounts of gas, and stars within the systems accrete gas individually. We show, however, that when the sound speed or the relative velocity of the ambient medium is less than the central velocity dispersion of the cluster, it is accreted into the collective potential of the cluster prior to being accreted onto the individual stars within the cluster. The collective rate is strongly enhanced relative to the individual rates. This effect may potentially modify the white dwarf cooling sequence in globular clusters with low-inclination and low-eccentricity Galactic orbits, and lead to the rejuvenation of some marginally surviving cores of globular clusters and nucleated dwarf galaxies near the Galactic center. Such effects will only occur rarely, bu...

Lin, Douglas N C

2007-01-01

69

Gas Accretion by Globular Clusters and Nucleated Dwarf Galaxies and the Formation of the Arches and Quintuplet Clusters  

E-print Network

We consider here the collective accretion of gas by globular clusters and dwarf galaxies moving through the interstellar medium. In the limit of high velocity and/or sound speed of the ISM, the collective potential of the cluster is insufficient to accrete significant amounts of gas, and stars within the systems accrete gas individually. We show, however, that when the sound speed or the relative velocity of the ambient medium is less than the central velocity dispersion of the cluster, it is accreted into the collective potential of the cluster prior to being accreted onto the individual stars within the cluster. The collective rate is strongly enhanced relative to the individual rates. This effect may potentially modify the white dwarf cooling sequence in globular clusters with low-inclination and low-eccentricity Galactic orbits, and lead to the rejuvenation of some marginally surviving cores of globular clusters and nucleated dwarf galaxies near the Galactic center. Such effects will only occur rarely, but may explain the existence of clusters of young, massive stars near the Galactic center.

Douglas N. C. Lin; Stephen D. Murray

2007-03-30

70

Sizes of nanobubbles from nucleation rate measurements  

NASA Astrophysics Data System (ADS)

In homogeneous bubble nucleation, the critical nucleus typically has nanometer dimensions. The volume V of a critical bubble can be determined from the simple equation (partial W/partial p)_T=V, where W is the reversible work of nucleus formation and p is the ambient pressure of the liquid phase in which bubble formation is occurring. The relation, W/kT=-ln J+ln A, where J is the steady state nucleation rate and A is the weakly pressure-dependent kinetic prefactor, allows V to be determined from rate measurements. The original derivation of this equation for V from the nucleation theorem was limited to one-component, ideal gas bubbles with a gas density much smaller than that of the ambient liquid. [D. Kashchiev, Nucleation: basic theory with applications (Butterworth-Heinemann, Oxford, 2000) p. 226.] The result is actually much more general, and it will be shown that it applies to multi-component, nonideal gas bubbles, provided the same density inequality holds. When the bubble phase and liquid densities are comparable, a more complicated, but also general and rigorous result is found.

Wilemski, G.

2003-03-01

71

Initial nucleation site formation due to acoustic droplet vaporization  

PubMed Central

Acoustic droplet vaporization (ADV) is the selective vaporization of liquid microdroplets using ultrasound, resulting in gas bubbles. The ADV process has been proposed as a tool in biomedical applications such as gas embolotherapy, drug delivery, and phase-change contrast agents. Using a 7.5?MHz focused transducer, the initial gas nucleus formed in perfluorocarbon microdroplets was directly visualized using ultra-high speed imaging. The experimental results of initial nucleation site location were compared to a 2D axisymmetric linear acoustic model investigating the focal spot of the acoustic wave within the microdroplets. Results suggest a wavelength to droplet diameter dependence on nucleation site formation. PMID:24711671

Li, David S.; Kripfgans, Oliver D.; Fabiilli, Mario L.; Brian Fowlkes, J.; Bull, Joseph L.

2014-01-01

72

Gas-phase Californium ion chemistry  

Microsoft Academic Search

The gas-phase chemistry of Cf+ was examined, this now being the heaviest element with which such studies have been performed. The emphasis was on the efficiency of dehydrogenation of alkenes by naked Cf+; direct comparison was made between the reactivities of Cf+ and those of Cm+, Pr+, and Tm+. The results with alkenes indicated that Cf+ is inefficient at C?H

John K. Gibson; Richard G. Haire

2000-01-01

73

EPA GAS PHASE CHEMISTRY CHAMBER STUDIES  

EPA Science Inventory

Gas-phase smog chamber experiments are being performed at EPA in order to evaluate a number of current chemical mechanisms for inclusion in EPA regulatory and research models. The smog chambers are 9000 L in volume and constructed of 2-mil teflon film. One of the chambers is co...

74

Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase  

NASA Astrophysics Data System (ADS)

Lysozyme, and most particularly the tetragonal form of the protein, has become the default standard protein for use in macromolecule crystal nucleation and growth studies. There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests this proteins crystal nucleation and growth is by addition of associated species that are preformed by standard reversible concentration-driven self association processes in the bulk solution. The evidence includes high resolution AFM studies of the surface packing and of growth unit size at incorporation, fluorescence resonance energy transfer measurements of intermolecular distances in dilute solution, dialysis kinetics, and modeling of the growth rate data. We have developed a selfassociation model for the proteins crystal nucleation and growth. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. Further, it indicates that nucleation and crystal growth are not distinct mechanistically, but identical, with the primary difference being the probability that the particle will continue to grow or dissolve. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small (M.W. = 14,400), a structured octamer in the 43 helix configuration (the proposed average sized growth unit) would have a M.W. = 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm commonly attach to the crystal. These measurements were made at approximately saturation conditions, and they reflect the sizes of species that both added or desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it will be oriented to some degree in a flowing boundary layer, even at the low flow velocities measured about macromolecule crystals. Flow-driven effects resulting in misorientation upon addition to and incorporation into the crystal need only be a small fraction of a percentage to significantly affect the resulting crystal. One Earth, concentration gradient driven flow will maintain a high interfacial concentration, i.e., a high level (essentially that of the bulk solution) of solute association at the interface and higher growth rate. Higher growth rates mean an increased probability that misaligned growth units are trapped by subsequent growth layers before they can be desorbed and try again, or that the desorbing species will be smaller than the adsorbing species. In microgravity the extended diffusive boundary layer will lower the interfacial concentration. This results in a net dissociation of aggregated species that diffuse in from the bulk solution, i.e., smaller associated species, which are more likely able to make multiple attempts to correctly bind, yielding higher quality crystals.

Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar

2002-11-01

75

Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase  

NASA Technical Reports Server (NTRS)

Lysozyme, and most particularly the tetragonal form of the protein, has become the default standard protein for use in macromolecule crystal nucleation and growth studies. There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests this proteins crystal nucleation and growth is by addition of associated species that are preformed by standard reversible concentration-driven self association processes in the bulk solution. The evidence includes high resolution AFM studies of the surface packing and of growth unit size at incorporation, fluorescence resonance energy transfer measurements of intermolecular distances in dilute solution, dialysis kinetics, and modeling of the growth rate data. We have developed a selfassociation model for the proteins crystal nucleation and growth. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. Further, it indicates that nucleation and crystal growth are not distinct mechanistically, but identical, with the primary difference being the probability that the particle will continue to grow or dissolve. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small (M.W. = 14,400), a structured octamer in the 4(sub 3) helix configuration (the proposed average sized growth unit) would have a M.W. = 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm commonly attach to the crystal. These measurements were made at approximately saturation conditions, and they reflect the sizes of species that both added or desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it will be oriented to some degree in a flowing boundary layer, even at the low flow velocities measured about macromolecule crystals. Flow-driven effects resulting in misorientation upon addition to and incorporation into the crystal need only be a small fraction of a percentage to significantly affect the resulting crystal. One Earth, concentration gradient driven flow will maintain a high interfacial concentration, i.e., a high level (essentially that of the bulk solution) of solute association at the interface and higher growth rate. Higher growth rates mean an increased probability that misaligned growth units are trapped by subsequent growth layers before they can be desorbed and try again, or that the desorbing species will be smaller than the adsorbing species. In microgravity the extended diffusive boundary layer will lower the interfacial concentration. This results in a net dissociation of aggregated species that diffuse in from the bulk solution, i.e., smaller associated species, which are more likely able to make multiple attempts to correctly bind, yielding higher quality crystals.

Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar

2002-01-01

76

Determining phase diagrams of gas-liquid systems using a microfluidic PVT.  

PubMed

A novel microfluidic device designed for analyzing phase diagrams of gas-liquid systems (PVT or pressure-volume-temperature measurements) is described. The method mimics the phase transition of a reservoir fluid as it travels through the wellbore from the formation to the surface. The device consists of a long serpentine microchannel etched in a silicon substrate. The local pressure inside the channel is measured using membrane-based optical pressure sensors positioned along the channel. Geometrical restrictions are placed along the microchannel in order to nucleate bubbles when nucleation conditions are met, thus preventing the development of a supersaturation state in the channel. We point out that a local equilibrium state between gas and liquid phases is achieved, which implies that equilibrium properties can be directly measured on the chip. We analyze different mixtures of hydrocarbon systems and, consistently with the preceding analysis, obtain excellent agreement between our technique and conventional measurements. From a practical viewpoint (important for the relevance of the technology), we observe that the measurement time of thermodynamic properties of gas-liquid systems is reduced from hours to minutes with the present device without compromising the measurement accuracy. PMID:22930353

Mostowfi, Farshid; Molla, Shahnawaz; Tabeling, Patrick

2012-11-01

77

Modeling of Nucleation Processes  

Microsoft Academic Search

Nucleation is the onset of a first-order phase transition by which a metastable phase transforms into a more stable one. Such a phase transition occurs when an initial system initially in equilibrium is destabilized by the change of an external parameter like the temperature or the pressure. If the perturbation is small enough, the system does not become unstable but

Emmanuel Clouet

2010-01-01

78

CARBON DIOXIDE SEPARATION BY PHASE ENHANCED GAS-LIQUID ABSORPTION  

SciTech Connect

A new process called phase enhanced gas-liquid absorption has been developed in its early stage. It was found that adding another phase into the absorption system of gas/aqueous phase could enhance the absorption rate. A system with three phases was studied. In the system, gas phase was carbon dioxide. Two liquid phases were used. One was organic phase. Another was aqueous phase. By addition of organic phase into the absorption system of CO{sub 2}-aqueous phase, the absorption rate of CO{sub 2} was increased significantly. CO{sub 2} finally accumulated into aqueous phase. The experimental results proved that (1) Absorption rate of carbon dioxide was enhanced by adding organic phase into gas aqueous phase system; (2) Organic phase played the role of transportation of gas solute (CO{sub 2}). Carbon dioxide finally accumulated into aqueous phase.

Liang Hu

2004-09-30

79

CARBON DIOXIDE SEPARATION BY PHASE ENHANCED GAS-LIQUID ABSORPTION  

SciTech Connect

A new process called phase enhanced gas-liquid absorption has been developed in its early stage. It was found that adding another phase into the absorption system of gas/aqueous phase could enhance the absorption rate. A system with three phases was studied. In the system, gas phase was carbon dioxide. Two liquid phases were used. One was organic phase. Another was aqueous phase. By addition of organic phase into the absorption system of CO{sub 2}-aqueous phase, the absorption rate of CO{sub 2} was increased significantly. CO{sub 2} finally accumulated into aqueous phase. The experimental results proved that (1) Absorption rate of carbon dioxide was enhanced by adding organic phase into gas aqueous phase system; (2) Organic phase played the role of transportation of gas solute (CO{sub 2}). Carbon dioxide finally accumulated into aqueous phase.

Liang Hu; Adeyinka A. Adeyiga

2004-05-01

80

Homogeneous vapor phase nucleation of a large fatty acid: Stearic acid  

NASA Astrophysics Data System (ADS)

Homogeneous nucleation measurements are made on stearic acid vapor using a diffusion cloud chamber and the resulting critical supersaturations compared with the predictions of the classical Becker-Doering theory. These measurements are difficult because of the unusually low pressures and high temperatures required to investigate the involatile stearic acid molecule. The results indicate a definite discrepancy between theory and experiment. Measured critical supersaturations lie 27% above the theory at the lowest temperature and 10% below the theory at the highest temperature. Calculations show that part of this increase in experimental critical supersaturation at the lower temperatures could be due to association in the vapor. There are two additional findings: (1) The usual top plate boundary condition must be corrected for molecules, such as stearic acid, which have low equilibrium vapor pressures in the temperature range of interest. (2) The growth times for stearic acid droplets are at the limits that can be tolerated in a feasible diffusion cloud chamber experiment. This study suggests an area for future investigation. Once the association equilibrium constant for stearic acid vapor is known, the data presented here can be reanalyzed and the extent to which the dimer stabilizes the supersaturated vapor determined.

Becker, Carol

1980-04-01

81

On radiative forcing of sulphate aerosol produced from ion-promoted nucleation mechanisms in an atmospheric global model  

Microsoft Academic Search

A significant fraction of the total number of particles present in the atmosphere is formed by nucleation in the gas phase.\\u000a Nucleation and the subsequent growth process influence both number concentration of particles and their size distribution\\u000a besides chemical and optical properties of atmospheric aerosols. Sulphate aerosol nucleation mechanisms promoted by ions have\\u000a been evaluated here in a tropospheric interactive

Hashmi FatimaH; H. C. Upadhyaya; S. N. Tripathi; O. P. Sharma; Fangqun Yu

2011-01-01

82

Phase separation in solid 3He4He mixtures: Comparison with theory of homogeneous nucleation  

Microsoft Academic Search

NMR and pressure have been measured in a solid 3He-4He mixture as the temperature was lowered in steps through phase separation. The spin-echo method was used to detect the behavior typical for bounded diffusion and to estimate the diffusion coefficient, size and cluster concentration in the 3He-enriched phase. The characteristic phase separation time constant of the mixture was found to

A. Smith; V. A. Maidanov; E. Ya. Rudavskii; V. N. Grigor'ev; V. V. Slezov; M. Poole; J. Saunders; B. Cowan

2003-01-01

83

Phases of a bilayer Fermi gas  

SciTech Connect

We investigate a two-species Fermi gas in which one species is confined in two parallel layers and interacts with the other species in the three-dimensional space by a tunable short-range interaction. Based on the controlled weak coupling analysis and the exact three-body calculation, we show that the system has a rich phase diagram in the plane of the effective scattering length and the layer separation. Resulting phases include an interlayer s-wave pairing, an intralayer p-wave pairing, a dimer Bose-Einstein condensation, and a Fermi gas of stable Efimov-like trimers. Our system provides a widely applicable scheme to induce long-range interlayer correlations in ultracold atoms.

Nishida, Yusuke [Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2010-07-15

84

Phases of a bilayer Fermi gas  

E-print Network

We investigate a two-species Fermi gas in which one species is confined in two parallel layers and interacts with the other species in the three-dimensional space by a tunable short-range interaction. Based on the controlled weak coupling analysis and the exact three-body calculation, we show that the system has a rich phase diagram in the plane of the effective scattering length and the layer separation. Resulting phases include an interlayer s-wave pairing, an intralayer p-wave pairing, a dimer Bose-Einstein condensation, and a Fermi gas of Efimov-like trimers. Our system provides a widely applicable scheme to induce long-range interlayer correlations in ultracold atoms.

Nishida, Yusuke

2009-01-01

85

Phases of a bilayer Fermi gas  

E-print Network

We investigate a two-species Fermi gas in which one species is confined in two parallel layers and interacts with the other species in the three-dimensional space by a tunable short-range interaction. Based on the controlled weak coupling analysis and the exact three-body calculation, we show that the system has a rich phase diagram in the plane of the effective scattering length and the layer separation. Resulting phases include an interlayer s-wave pairing, an intralayer p-wave pairing, a dimer Bose-Einstein condensation, and a Fermi gas of stable Efimov-like trimers. Our system provides a widely applicable scheme to induce long-range interlayer correlations in ultracold atoms.

Yusuke Nishida

2010-07-12

86

Gas-Phase Photoionization Of A Protein  

NASA Astrophysics Data System (ADS)

We present preliminary results on gas phase photoionization of electrosprayproduced multiply protonated cytochrome c protein (104 amino acids; Ë?12.4 kDa), which has been achieved with a newly developed experimental system for spectroscopy of electrosprayed ions in a linear quadrupole ion trap using a monochromatized vacuum ultraviolet (VUV) synchrotron radiation and tandem mass spectrometry method. The investigation of proteins in the gas phase, where they are free of the influence of counterions and solvent molecules, offer a possibility to understand their intrinsic molecular properties. However, due to limited both ion densities and available number of photons, the use of synchrotron radiation for the trapped ions spectroscopy is a rather challenging task. The feasibility of coupling a Fourier transform ion cyclotron resonance ion trap with soft x-ray synchrotron beamline and the first successful use of synchrotron radiation for spectroscopy of electrosprayed negative ions stored in a three-dimensional quadrupole ion trap have been demonstrated only recently (R. Thissen et al., 2008, Phys. Rev. Lett., 100, 223001; A. Giulliani et al., Proc. 57th ASMS Conf., Philadelphia, 2009). The present results are the first reported on photoionization of kDa species in the gas phase and are valuable regarding both a fundamental interest of accessing physical properties of large biological ions isolated in vacuo and potential development of a new technique for proteomics.

Milosavljevic, A. R.; Giuliani, A.; Nicolas, C.; Gil, J.-F.; Lemaire, J.; Refregiers, M.; Nahon, L.

2010-07-01

87

Fuel Performance Experiments and Modeling: Fission Gas Bubble Nucleation and Growth in Alloy Nuclear Fuels  

SciTech Connect

Advanced fast reactor systems being developed under the DOE's Advanced Fuel Cycle Initiative are designed to destroy TRU isotopes generated in existing and future nuclear energy systems. Over the past 40 years, multiple experiments and demonstrations have been completed using U-Zr, U-Pu-Zr, U-Mo and other metal alloys. As a result, multiple empirical and semi-empirical relationships have been established to develop empirical performance modeling codes. many mechamistic questions about fission as mobility, bubble coalescience, and gas release have been answered through industrial experience, reearch, and empirical understanding. The advent of modern computational materials science, however, opens new doors of development such that physics-based multi-scale models may be developed to enable a new generation of predictive fuel performance codes that are not limited by empiricism.

McDeavitt, Sean; Shao, Lin; Tsvetkov, Pavel; Wirth, Brian; Kennedy, Rory

2014-04-07

88

Isothermal nucleation and growth kinetics of Pd/Ag alloy phase via in-situ time-resolved high-temperature x-ray diffraction (HTXRD) analysis  

SciTech Connect

Among several different approaches to form Pd/Ag alloys for hydrogen separation applications, ex-situ studies carried by conventional X-ray point scanning detectors might fail to reveal the key aspects of the phase transformation between Pd and Ag metals. In this respect, in-situ time-resolved high temperature X-ray diffraction (HTXRD) was employed to study the Pd/Ag alloy phase nucleation and growth kinetics. By the use of linear position sensitive detectors, advanced optics and profile fitting with the use of JADE-6.5 software, isothermal phase evolution of the Pd/Ag alloy at 500 C, 550 C and 600 C under hydrogen atmosphere were quantified to elucidate the mechanistic details of the Pd/Ag alloy phase nucleation and growth pattern. Analysis of the HTXRD data by the Avrami model indicated that the nucleation of the Pd/Ag alloy phase was instantaneous where the growth mechanism was through diffusion-controlled one-dimensional thickening of the Pd/Ag alloy layer. The value of the Avrami exponent, n, was found to increase with temperature with the values of 0.34, 0.39 and 0.67 at 500oC, 550oC and 600oC, respectively. In addition, parabolic rate law analysis suggested that the nucleation of the Pd/Ag alloy phase was through a heterogeneous nucleation mode, in which the nucleation sites were defined as the non-equilibrium defects. The cross-sectional SEI micrographs indicated that the Pd/Ag alloy phase growth was strongly dependent upon the deposition morphology of the as-synthesized Pd and Ag layers formed by the electroless plating. Based on the Avrami model and the parabolic rate law, the estimated activation energies for the phase transformation were 236.5 and 185.6 kJ/mol and in excellent agreement with the literature values (183-239.5 kJ/mol).

Ayturk, Mahmut Engin [Worcester Polytechnic Institute; Payzant, E Andrew [ORNL; Speakman, Scott A [ORNL; Ma, Yi Hua [Worcester Polytechnic Institute

2008-01-01

89

Infrared spectroscopy of homogeneously nucleated hydrazine aerosols - Disordered and crystalline phases  

NASA Astrophysics Data System (ADS)

It is shown that aerosols generated at low temperatures and high condensation rate spontaneously form in a highly crystalline state. The resonant absorption bands in the IR spectra of these highly crystalline particles are much sharper than any reported previously in the bulk, and reveal details in the N-H vibrational bands that have not been previously observed. A disordered phase is also observed at somewhat higher temperatures. These results are consistent with this being a supercooled liquid. The fact that the spectra associated with these two aerosol phases are quite different is important to any future attempts at detecting hydrazine aerosols in planetary atmospheres by remote sensing techniques.

Dunder, T.; Clapp, M. L.; Miller, R. E.

1993-01-01

90

Infrared spectroscopy of homogeneously nucleated hydrazine aerosols - Disordered and crystalline phases. [in planetary atmospheres  

NASA Technical Reports Server (NTRS)

It is shown that aerosols generated at low temperatures and high condensation rate spontaneously form in a highly crystalline state. The resonant absorption bands in the IR spectra of these highly crystalline particles are much sharper than any reported previously in the bulk, and reveal details in the N-H vibrational bands that have not been previously observed. A disordered phase is also observed at somewhat higher temperatures. These results are consistent with this being a supercooled liquid. The fact that the spectra associated with these two aerosol phases are quite different is important to any future attempts at detecting hydrazine aerosols in planetary atmospheres by remote sensing techniques.

Dunder, T.; Clapp, M. L.; Miller, R. E.

1993-01-01

91

Carbon phases versus hydrogen phases: neutral gas in nearby galaxies  

NASA Astrophysics Data System (ADS)

Due to its lower-than-hydrogen first ionization energy, atomic carbon is ionized throughout the diffuse ISM, tracing both regions of ioinized and neutral hydrogen gas. On the other hand, carbon monoxide (CO) exists and emits exclusively where hydrogen is in molecular form. Neutral atomic carbon is predicted to exist in between these phases, but recent evidence in our Galaxy and from simulations show it may be closely tied to the molecular gas than previously thought. Here, we investigate the gas in various carbon stages (evidenced through emission in [CII], [CI] and CO) compared to hydrogen stages (through ?CO-corrected CO for H2 and HI emission). The observations are based upon the Beyond the Peak sample of 22 galaxies with data from the Herschel Space Observatory SPIRE FTS instrument, as well as relying on ground-based CO and HI observations. Based on these comparisons, [CI] does trace CO well and thus may provide a good way to trace molecular gas in external galaxies as well as in molecular clouds in the Milky Way.

Crocker, Alison Faye; Pellegrini, Eric; Smith, John-David T.; Beyond the Peak Team

2015-01-01

92

Gas phase thermochemistry of organogermanium compounds  

SciTech Connect

A variety of silyl- and alkyl-germylene precursors have been synthesized and subsequently pyrolyzed in the gas phase. Arrhenius parameters were obtained employing a pulsed-stirred flow reactor for these unimolecular decompositions. These precursors are divided into two major categories by mechanism of germylene extrusion: {alpha}-elimination precursors and germylacetylenes. The extrusion of germylenes from germylacetylene precursors is of primary interest. A mechanism is proposed employing a germacyclopropene intermediate. Evidence supporting this mechanism is presented. In the process of exploring germylacetylenes as germylene precursors, an apparent dyatropic rearrangement between germanium and silicon was observed. This rearrangement was subsequently explored.

Engel, J.P.

1993-12-07

93

Cold core gas-phase chemical model  

NASA Astrophysics Data System (ADS)

This model written in Fortran77 can be used to compute the gas-phase chemical evolution of a dense molecular cloud at a fixed temperature and density. The model is adapted for the osu.2005 (https://www.physics.ohio-state.edu/~eric/research.html) chemical database of Eric Herbst (Ohio State University, USA) but can be modified to read any network. The model contains an option to compute the uncertainties of the modeled abundances. The method for the uncertainty calculation is explained in Wakelam et al. (2005).

Wakelam, V.

2006-11-01

94

Giddings Austin chalk enters deep lean-gas phase  

SciTech Connect

Deep lean gas is the latest phase in the growth of the Giddings field Austin chalk play. The first phase involved drilling vertical oil and gas wells. Next came the horizontal well boom in the shallower Austin chalk area, which is still continuing. And now this third phase places horizontal laterals in the Austen chalk at about 14,000--15,000 ft to produce lean gas. The article describes the producing wells and gas gathering.

Moritis, G.

1995-12-25

95

Vaccum Gas Tungsten Arc Welding, phase 1  

NASA Technical Reports Server (NTRS)

This two year program will investigate Vacuum Gas Tungsten Arc Welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. VGTAW appears to offer a significant improvement in weldability because of the clean environment and lower heat input needed. The overall objective of the program is to develop the VGTAW technology and implement it into a manufacturing environment that will result in lower cost, better quality and higher reliability aerospace components for the space shuttle and other NASA space systems. Phase 1 of this program was aimed at demonstrating the process's ability to weld normally difficult-to-weld materials. Phase 2 will focus on further evaluation, a hardware demonstration and a plan to implement VGTAW technology into a manufacturing environment. During Phase 1, the following tasks were performed: (1) Task 11000 Facility Modification - an existing vacuum chamber was modified and adapted to a GTAW power supply; (2) Task 12000 Materials Selection - four difficult-to-weld materials typically used in the construction of aerospace hardware were chosen for study; (3) Task 13000 VGTAW Experiments - welding experiments were conducted under vacuum using the hollow tungsten electrode and evaluation. As a result of this effort, two materials, NARloy Z and Incoloy 903, were downselected for further characterization in Phase 2; and (4) Task 13100 Aluminum-Lithium Weld Studies - this task was added to the original work statement to investigate the effects of vacuum welding and weld pool vibration on aluminum-lithium alloys.

Weeks, J. L.; Krotz, P. D.; Todd, D. T.; Liaw, Y. K.

1995-01-01

96

Gas phase hyper-Rayleigh scattering measurements  

NASA Astrophysics Data System (ADS)

Measurements of hyper-Rayleigh scattering intensities and polarization ratios are presented for nine small molecules in the gas phase [CH4, CF4, CCl4, N2O, NH3, D2O, SO2, CF2Cl2, and (CH3)2CO]. In four cases [CH4, CF4, CCl4, and N2O] all molecular hyperpolarizability tensor components can be determined from the measurements. The results of this experiment are compared with the results of previous ab initio calculations, finding discrepancies up to 60%. Including vibrational contributions decreases the discrepancies for CH4 and CF4 and increases them for CCl4, D2O, and NH3.

Shelton, David P.

2012-07-01

97

Analysis of Ni nanoparticle gas phase sintering  

NASA Astrophysics Data System (ADS)

The sintering of Ni nanoparticle agglomerates in the gas phase is studied. The partially or completely sintered agglomerates are characterized in flight by in situ electrical mobility measurement and after their deposition by transmission electron microscopy. The mobility diameter, the mean primary particle diameter, and the total surface area of the agglomerates are determined as functions of the sintering temperature. The experimental results are analyzed using an empirical law for the primary particle coarsening as well as by means of a modified Koch-Friedlander theory. It turns out that the activation energy for the dominating diffusion process is Ea=0.6eV/atom , which is characteristic for surface diffusion in Ni. Our analysis provides a consistent picture with respect to both the temperature dependence of the characteristic sintering time and the mean diffusion length.

Tsyganov, Sergej; Kästner, Jochen; Rellinghaus, Bernd; Kauffeldt, Thomas; Westerhoff, Frank; Wolf, Dietrich

2007-01-01

98

Gas-phase thermochemistry of chloropyridines  

NASA Astrophysics Data System (ADS)

The gas-phase standard molar enthalpy of formation of the 2,3,5-trichloropyridine compound was derived from the enthalpies of combustion of the crystalline solid measured by rotating-bomb calorimetry and its enthalpy of sublimation obtained by Calvet microcalorimetry at T = 298.15 K. The standard enthalpies of formation for this compound and for the other chlorosubstituted pyridines were determined by DFT calculations. The experimental enthalpy of formation of 2,3,5-trichloropyridine is (65.8 ± 2.3) kJ mol -1, in excellent agreement with the B3LYP/6-311+G(2d,2p)//B3LYP/6-31G(d) value. The affinity of pyridine to some metal cations was also calculated at the same DFT level of theory and compared with experimental data.

Gomes, José R. B.; Amaral, Luísa M. P. F.; Ribeiro da Silva, Manuel A. V.

2005-04-01

99

Transferring pharmaceuticals into the gas phase  

NASA Astrophysics Data System (ADS)

The dissolution of molecules of biological interest in supercritical carbon dioxide is investigated using pulsed molecular beam mass spectrometry. Due to the mild processing temperatures of most supercritical fluids, their adiabatic expansion into vacuum permits to transfer even thermally very sensitive substances into the gas phase, which is particularly attractive for pharmaceutical and biomedical applications. In addition, supercritical CO2constitutes a chemically inert solvent that is compatible with hydrocarbon-free ultrahigh vacuum conditions. Here, we report on the dissolution and pulsed supersonic jet expansion of caffeine (C8H10N4O2), the provitamin menadione (C11H8O2), and the amino acid derivative l-phenylalanine tert-butyl ester hydrochloride (C6H5CH2CH(NH2)COOC(CH3)3[dot operator]HCl), into vacuum. An on-axis residual gas analyzer is used to monitor the relative amounts of solute and solvent in the molecular beam as a function of solvent densityE The excellent selectivity and sensitivity provided by mass spectrometry permits to probe even trace amounts of solutes. The strong density variation of CO2 close to the critical point results in a pronounced pressure dependence of the relative ion currents of solute and solvent molecules, reflecting a substantial change in solubility.

Christen, Wolfgang; Krause, Tim; Rademann, Klaus

2008-11-01

100

Gas: A Neglected Phase in Remediation of Metals and Radionuclides  

SciTech Connect

The gas phase is generally ignored in remediation of metals and radionuclides because it is assumed that there is no efficient way to exploit it. In the literal sense, all remediations involve the gas phase because this phase is linked to the liquid and solid phases by vapor pressure and thermodynamic relationships. Remediation methods that specifically use the gas phase as a central feature have primarily targeted volatile organic contaminants, not metals and radionuclides. Unlike many organic contaminants, the vapor pressure and Henry's Law constants of metals and radionuclides are not generally conducive to direct air stripping of dissolved contaminants. Nevertheless, the gas phase can play an important role in remediation of inorganic contaminants and provide opportunities for efficient, cost effective remediation. The objective here is to explore ways in which manipulation of the gas phase can be used to facilitate remediation of metals and radionuclides.

Denham, Miles E.; Looney, Brian B

2005-09-28

101

Nucleation at the Contact Line Observed on Nanotextured Surfaces  

NASA Astrophysics Data System (ADS)

It has been conjectured that roughness plays a role in surface nucleation, the tendency for freezing to begin preferentially at the liquid-gas interface. Using high speed imaging, we sought evidence for freezing at the contact line on catalyst substrates with imposed characteristic length scales (texture). Length scales consistent with the critical nucleus size and with ? ˜? /? , where ? is a relevant line tension and ? is the surface tension, range from nanometers to micrometers. It is found that nanoscale texture causes a shift in the nucleation of ice in supercooled water to the three-phase contact line, while microscale texture does not.

Gurganus, C. W.; Charnawskas, J. C.; Kostinski, A. B.; Shaw, R. A.

2014-12-01

102

Nucleation at the contact line observed on nanotextured surfaces.  

PubMed

It has been conjectured that roughness plays a role in surface nucleation, the tendency for freezing to begin preferentially at the liquid-gas interface. Using high speed imaging, we sought evidence for freezing at the contact line on catalyst substrates with imposed characteristic length scales (texture). Length scales consistent with the critical nucleus size and with ???/?, where ? is a relevant line tension and ? is the surface tension, range from nanometers to micrometers. It is found that nanoscale texture causes a shift in the nucleation of ice in supercooled water to the three-phase contact line, while microscale texture does not. PMID:25526136

Gurganus, C W; Charnawskas, J C; Kostinski, A B; Shaw, R A

2014-12-01

103

Nucleation in the presence of long-range interactions. [performed on ferroelectric barium titanate  

NASA Technical Reports Server (NTRS)

Unlike droplet nucleation near a liquid-gas critical point, the decay of metastable phases in crystalline materials is strongly affected by the presence of long-range forces. Field quench experiments performed on the ferroelectric barium titanate indicate that nucleation in this material is markedly different from that observed in liquids. In this paper, a theory for nucleation at a first-order phase transition in which the mediating forces are long range is presented. It is found that the long-range force induces cooperative nucleation and growth processes, and that this feedback mechanism produces a well-defined delay time with a sharp onset in the transformation to the stable phase. Closed-form expressions for the characteristic onset time and width of the transition are developed, in good agreement with numerical and experimental results.

Chandra, P.

1989-01-01

104

Experiments on Nucleation in Different Flow Regimes  

NASA Technical Reports Server (NTRS)

The vast majority of metallic engineering materials are solidified from the liquid phase. Understanding the solidification process is essential to control microstructure, which in turn, determines the properties of materials. The genesis of solidification is nucleation, where the first stable solid forms from the liquid phase. Nucleation kinetics determine the degree of undercooling and phase selection. As such, it is important to understand nucleation phenomena in order to control solidification or glass formation in metals and alloys.

Bayuzick, Robert J.; Hofmeister, W. H.; Morton, C. M.; Robinson, M. B.

1998-01-01

105

Buckyball Nucleation of HiPco Tubes  

NASA Technical Reports Server (NTRS)

The purpose of this innovation is to enhance nucleation of single-wall nanotubes (SWNTs) in the HiPco process, selectively producing 10,10 tubes, something which until now has not been thought possible. This is accomplished by injecting C60, or a derivative of C60, solubilized in supercritical CO2 together with a transition metal carboneal cocatalyst into the HiPco reactor. This is a variant on the supercritical disclosure. C60 has never been used to nucleate carbon nanotubes in the gas phase. C60 itself may not have adequate solubility in supercritical CO2. However, fluorinated C60, e.g., C60F36, is easy to make cheaply and should have much enhanced solubility.

Smalley, Richard E.

2012-01-01

106

SHORT COMMUNICATION Gas-Phase Separations of Protease Digests  

E-print Network

SHORT COMMUNICATION Gas-Phase Separations of Protease Digests Stephen J. Valentine, Anne E University, Bloomington, Indiana, USA A mixture of peptides from a complete tryptic digest of ubiquitin has and identify peptides from a tryptic digest of ubiquitin. The mixture was electrosprayed into the gas phase

Clemmer, David E.

107

On Immersion Freezing as a Nucleation Mechanism in Mixed-Phase Stratus Gijs de Boer, Tempei Hashino,Gregory J.Tripoli and Edwin W.Eloranta  

E-print Network

courtesy of J.P.Blanchet (From Bigg,1980) - Bigg (1980) observed sulfuric acid coating on aero- sol particl,condensation and deposi- tion freezing are not primarily responsible for ice production, as all require free Nucleation Contact Nucleation Depositional Nucleation Immersion Nucleation So which one drives ice production

Eloranta, Edwin W.

108

Gamma-ray spectra of hexane in gas phase and liquid phase  

E-print Network

Theoretical gamma-ray spectra of molecule hexane have been calculated and compared with the experimental results in both gas (Surko et al, 1997) and liquid (Kerr et al, 1965) phases. The present study reveals that in gas phase not all valence electrons of hexane exhibit the same probability to annihilate a positron. Only the positrophilic electrons in the valence space dominate the gamma-ray spectra, which are in good agreement with the gas phase measurement. When hexane is confined in liquid phase, however, the intermolecular interactions ultimately eliminate the free molecular orientation and selectivity for the positrophilic electrons in the gas phase. As a result, the gamma-ray spectra of hexane become an averaged contribution from all valence electrons, which is again in agreement with liquid phase measurement. The roles of the positrophilic electrons in annihilation process for gas and liquid phases of hexane have been recognized for the first time in the present study.

Ma, Xiaoguang

2012-01-01

109

Gamma-ray spectra of hexane in gas phase and liquid phase  

E-print Network

Theoretical gamma-ray spectra of molecule hexane have been calculated and compared with the experimental results in both gas (Surko et al, 1997) and liquid (Kerr et al, 1965) phases. The present study reveals that in gas phase not all valence electrons of hexane exhibit the same probability to annihilate a positron. Only the positrophilic electrons in the valence space dominate the gamma-ray spectra, which are in good agreement with the gas phase measurement. When hexane is confined in liquid phase, however, the intermolecular interactions ultimately eliminate the free molecular orientation and selectivity for the positrophilic electrons in the gas phase. As a result, the gamma-ray spectra of hexane become an averaged contribution from all valence electrons, which is again in agreement with liquid phase measurement. The roles of the positrophilic electrons in annihilation process for gas and liquid phases of hexane have been recognized for the first time in the present study.

Xiaoguang Ma; Feng Wang

2012-11-01

110

Spaceborne lidar observations of the ice-nucleating potential of dust, polluted dust, and smoke aerosols in mixed-phase clouds  

NASA Astrophysics Data System (ADS)

Previous laboratory studies and in situ measurements have shown that dust particles possess the ability to nucleate ice crystals, and smoke particles to some extent as well. Even with coatings of pollutants such as sulphate and nitrate on the surface of dust particles, it has been shown that polluted dust particles are still able to nucleate ice in the immersion, deposition, condensation, and contact freezing modes, albeit less efficiently than unpolluted dust. The ability of these aerosols to act as ice nuclei in the Earth's atmosphere has important implications for the Earth's radiative budget and hence global climate change. Here we determine the relationship between cloud thermodynamic phase and dust, polluted dust, and smoke aerosols individually by analyzing their vertical profiles over a ˜5 year period obtained by NASA's spaceborne lidar, Cloud-Aerosol Lidar with Orthogonal Polarization. We found that when comparing the effects of temperature and aerosols, temperature appears to have the dominant influence on supercooled liquid cloud fraction. Nonetheless, we found that aerosols still appear to exert a strong influence on supercooled liquid cloud fraction as suggested by the existence of negative temporal and spatial correlations between supercooled liquid cloud fraction and frequencies of dust aerosols from around the world, at the -10°C, -15°C, -20°C, and -25°C isotherms. Although smoke aerosol frequencies were also found to be negatively correlated with supercooled liquid cloud fraction, their correlations are weaker in comparison to those between dust frequencies and supercooled liquid cloud fraction. For the first time, we show this based on observations from space, which lends support to previous studies that dust and potentially smoke aerosols can globally alter supercooled liquid cloud fraction. Our results suggest that the ice-nucleating ability of these aerosols may have an indirect climatic impact that goes beyond the regional scale, by influencing cloud thermodynamic phase globally.

Tan, Ivy; Storelvmo, Trude; Choi, Yong-Sang

2014-06-01

111

Gas-Liquid Flows and Phase Separation  

NASA Technical Reports Server (NTRS)

Common issues for space system designers include:Ability to Verify Performance in Normal Gravity prior to Deployment; System Stability; Phase Accumulation & Shedding; Phase Separation; Flow Distribution through Tees & Manifolds Boiling Crisis; Heat Transfer Coefficient; and Pressure Drop.The report concludes:Guidance similar to "A design that operates in a single phase is less complex than a design that has two-phase flow" is not always true considering the amount of effort spent on pressurizing, subcooling and phase separators to ensure single phase operation. While there is still much to learn about two-phase flow in reduced gravity, we have a good start. Focus now needs to be directed more towards system level problems .

McQuillen, John

2004-01-01

112

Recent progress in understanding particle nucleation and growth  

PubMed Central

In the past half decade, several new tools have become available for investigating particle nucleation and growth. A number of joint field and laboratory studies exploiting some of these new measurement capabilities will be described and new insights shared. the ability to measure OH, SO2, H2SO4 and aerosol number and size distributions has made possible a comparison between H2SO4 production and loss onto particles in continental air masses. In regions remote from urban emissions, agreement is typically quite good. In contrast, joint field measurements of nucleation precursors such as gas phase H2SO4 and ultrafine particles suggest that classical bimolecular nucleation theory may not properly describe the tropospheric nucleation process. An alternative mechanism, possibly involving ammonia as a stabilizing agent for H2SO4/H2O molecular clusters is discussed. Finally, ultrafine particle measurements are shown to offer new opportunities for studying particle growth rates. Preliminary results suggest that in a remote continental air mass, gas phase H2SO4 uptake is far too slow to explain observed growth rates.

Eisele, F. L.; McMurry, P. H.

1997-01-01

113

Entropydriven phase transitions in multitype lattice gas models  

E-print Network

--Rowlinson lattice gas, plane­rotor model, ferrofluid, percolation, chessboard estimate, reflection positivity. 1 energy and entropy attain a balance leading to the coexistence of high­ and low­temperature phases

114

Mixed Stationary Liquid Phases for Gas-Liquid Chromatography.  

ERIC Educational Resources Information Center

Describes a laboratory technique for use in an undergraduate instrumental analysis course that, using the interpretation of window diagrams, prepares a mixed liquid phase column for gas-liquid chromatography. A detailed procedure is provided. (BT)

Koury, Albert M.; Parcher, Jon F.

1979-01-01

115

Gas phase reaction of sulfur trioxide with water vapor  

Microsoft Academic Search

Sulfur trioxide (SO3) has long been known to react with water to produce sulfuric acid (H2S04). It has been commonly assumed that the gas phase reaction in the Earth`s atmosphere between SO3 and water vapor to produce sulfuric acid vapor is an important step in the production of sulfuric acid aerosol particles. The kinetics of the gas phase reaction of

C. E. Kolb; M. J. Molina; J. T. Jayne; R. F. Meads; D. R. Worsnop; A. A. Viggiano

1994-01-01

116

The gas phase oxidation of elemental mercury by ozone  

Microsoft Academic Search

The gas phase reaction between elemental mercury (Hg0) and ozone (03) has been studied in sunlight, in darkness, at different temperatures, and different surface-to-volume (s\\/v) ratios. At 03 concentrations above 20 ppm, a loss of Hg0 and a simultaneous formation of oxidized mercury (Hg(II)) was observed. The results suggest a partly heterogeneous reaction, with a gas phase rate constant of

B. Hall

1995-01-01

117

Liquid-Liquid Transition at Tg and Stable-Glass Phase Nucleation Rate Maximum at the Kauzmann Temperature TK  

E-print Network

An undercooled liquid is unstable. The driving force of the glass transition at Tg is a change of the undercooled-liquid Gibbs free energy. The classical Gibbs free energy change for a crystal formation is completed including an enthalpy saving. The crystal growth critical nucleus is used as a probe to observe the Laplace pressure change Dp accompanying the enthalpy change -Vm*Dp at Tg where Vm is the molar volume. A stable glass-liquid transition model predicts the specific heat jump of fragile liquids at temperatures smaller than Tg, the Kauzmann temperature TK where the liquid entropy excess with regard to crystal goes to zero, the equilibrium enthalpy between TK and Tg, the maximum nucleation rate at TK of superclusters containing magic atom numbers, and the equilibrium latent heats at Tg and TK. Strong-to-fragile and strong-to-strong liquid transitions at Tg are also described and all their thermodynamic parameters are determined from their specific heat jumps. The existence of fragile liquids quenched in the amorphous state, which do not undergo liquid-liquid transition during heating preceding their crystallization, is predicted. Long ageing times leading to the formation at TK of a stable glass composed of superclusters containing up to 147 atoms, touching and interpenetrating, are evaluated from nucleation rates.

Robert Felix Tournier

2014-04-25

118

Resonant Nucleation  

E-print Network

We investigate the role played by fast quenching on the decay of metastable (or false vacuum) states. Instead of the exponentially-slow decay rate per unit volume, $\\Gamma_{\\rm HN} \\sim \\exp[-E_b/k_BT]$ ($E_b$ is the free energy of the critical bubble), predicted by Homogeneous Nucleation theory, we show that under fast enough quenching the decay rate is a power law $\\Gamma_{\\rm RN} \\sim [E_b/k_BT]^{-B}$, where $B$ is weakly sensitive to the temperature. For a range of parameters, large-amplitude oscillations about the metastable state trigger the resonant emergence of coherent subcritical configurations. Decay mechanisms for different $E_b$ are proposed and illustrated in a (2+1)-dimensional scalar field model.

Marcelo Gleiser; Rafael Howell

2005-03-16

119

Loitering phase in brane gas cosmology  

Microsoft Academic Search

Brane gas cosmology (BGC) is an approach to M-theory cosmology in which the initial state of the Universe is taken to be small, dense and hot, with all fundamental degrees of freedom near thermal equilibrium. Such a starting point is in close analogy with the standard big bang (SBB) model. The topology of the Universe is assumed to be toroidal

Robert Brandenberger; Damien A. Easson; Dagny Kimberly

2002-01-01

120

High resolution ion mobility measurements for gas phase proteins: correlation between solution phase and gas phase conformations  

NASA Astrophysics Data System (ADS)

Our high resolution ion mobility apparatus has been modified by attaching an electrospray source to perform measurements for biological molecules. While the greater resolving power permits the resolution of more conformations for BPTI and cytochrome c, the resolved features are generally much broader than expected for a single rigid conformation. A major advantage of the new experimental configuration is the much gentler introduction of ions into the drift tube, so that the observed gas phase conformations appear to more closely reflect those present in solution. For example, it is possible to distinguish between the native state of cytochrome c and the methanol-denatured form on the basis of the ion mobility measurements; the mass spectra alone are not sensitive enough to detect this change. Thus this approach may provide a quick and sensitive tool for probing the solution phase conformations of biological molecules.

Hudgins, Robert R.; Woenckhaus, Jürgen; Jarrold, Martin F.

1997-11-01

121

Phase correction of a laser beam by gas jets  

Microsoft Academic Search

When a laser beam propagates in the atmosphere, its phase can be distorted either passively, due to turbulence, or actively, due to thermal blooming. It has been demonstrated that it is possible to partially compensate for these phase errors by physically distorting the transmitting optics. One aspect of another method is studied where the correcting active elements are gas jets

E. Wasserstrom; W. H. Christiansen

1981-01-01

122

Constant volume gas cell optical phase-shifter  

DOEpatents

A constant volume gas cell optical phase-shifter, particularly applicable for phase-shifting interferometry, contains a sealed volume of atmospheric gas at a pressure somewhat different than atmospheric. An optical window is present at each end of the cell, and as the length of the cell is changed, the optical path length of a laser beam traversing the cell changes. The cell comprises movable coaxial tubes with seals and a volume equalizing opening. Because the cell is constant volume, the pressure, temperature, and density of the contained gas do not change as the cell changes length. This produces an exactly linear relationship between the change in the length of the gas cell and the change in optical phase of the laser beam traversing it. Because the refractive index difference between the gas inside and the atmosphere outside is very much the same, a large motion must be made to change the optical phase by the small fraction of a wavelength that is required by phase-shifting interferometry for its phase step. This motion can be made to great fractional accuracy.

Phillion, Donald W. (Dublin, CA)

2002-01-01

123

Superfluid phases of the three-species fermion gas  

SciTech Connect

We discuss the zero temperature phase diagram of a dilute gas with three fermionic species. We make use of solvable limits to conjecture the behavior of the system in the 'unitary' regions. The physics of the Thomas-Efimov effect plays a role in these considerations. We find a rich phase diagram with superfluid, gapless superfluid and inhomogeneous phases with different symmetry breaking patterns. We then discuss one particular possible experimental implementation in a system of {sup 6}Li atoms and the possible phases arising in this system as an external magnetic field is varied across three overlapping Feshbach resonances. We also suggest how to experimentally distinguish the different phases.

Bedaque, Paulo F. [Lawrence-Berkeley Laboratory, Berkeley, CA 94720 (United States); University of Maryland, College Park, MD 20742 (United States)], E-mail: bedaque@umd.edu; D'Incao, Jose P. [Department of Physics, Kansas State University, Manhattan, KS 66506 (United States)], E-mail: jpdincao@jila.colorado.edu

2009-08-15

124

Communication: Fourier-transform infrared probing of remarkable quantities of gas trapped in cold homogeneously nucleated nanodroplets.  

PubMed

Studies of catalyzed all-vapor gas-hydrate formation on a sub-second timescale have been extended with a special focus on liquid-droplet compositions at the instant of hydrate crystallization. This focus has been enabled by inclusion of methanol in the all-vapor mixture. This slows droplet to gas-hydrate conversion near 200 K to a time scale suited for standard FTIR sampling. Such droplet data are sought as a guide to ongoing efforts to reduce the amount of guest catalyst required for instant formation of the gas hydrates. For the same reason, all-vapor sampling has also been extended to the generation of long-lived liquid droplets with reduced or no water content. Observations of single-solvent droplets show that surprising quantities of gas molecules are trapped during rapid droplet growth. For example, CO2 is trapped at levels near 50 mol. % in droplets of acetone, tetrahydrofuran, or trimethylene oxide formed under CO2 pressures of several Torr in a cold-chamber at 170 K. Less but significant amounts of gas are trapped at higher temperatures, or in methanol or water-methanol droplets. The droplet metastability appears to commonly lead to formation of bubbles larger than the original nanodroplets. Besides serving as a guide for the all-vapor gas-hydrate studies, the semiquantitative evidence of extensive trapping of gases is expected to have a role in future studies of atmospheric aerosols. PMID:23862921

Uras-Aytemiz, Nevin; Devlin, J Paul

2013-07-14

125

Communication: Fourier-transform infrared probing of remarkable quantities of gas trapped in cold homogeneously nucleated nanodroplets  

NASA Astrophysics Data System (ADS)

Studies of catalyzed all-vapor gas-hydrate formation on a sub-second timescale have been extended with a special focus on liquid-droplet compositions at the instant of hydrate crystallization. This focus has been enabled by inclusion of methanol in the all-vapor mixture. This slows droplet to gas-hydrate conversion near 200 K to a time scale suited for standard FTIR sampling. Such droplet data are sought as a guide to ongoing efforts to reduce the amount of guest catalyst required for instant formation of the gas hydrates. For the same reason, all-vapor sampling has also been extended to the generation of long-lived liquid droplets with reduced or no water content. Observations of single-solvent droplets show that surprising quantities of gas molecules are trapped during rapid droplet growth. For example, CO2 is trapped at levels near 50 mol. % in droplets of acetone, tetrahydrofuran, or trimethylene oxide formed under CO2 pressures of several Torr in a cold-chamber at 170 K. Less but significant amounts of gas are trapped at higher temperatures, or in methanol or water-methanol droplets. The droplet metastability appears to commonly lead to formation of bubbles larger than the original nanodroplets. Besides serving as a guide for the all-vapor gas-hydrate studies, the semiquantitative evidence of extensive trapping of gases is expected to have a role in future studies of atmospheric aerosols.

Uras-Aytemiz, Nevin; Devlin, J. Paul

2013-07-01

126

Development and evaluation of the aerosol dynamics and gas phase chemistry model ADCHEM  

NASA Astrophysics Data System (ADS)

The aim of this work was to develop a model suited for detailed studies of aerosol dynamics, gas and particle phase chemistry within urban plumes, from local scale (1 × 1 km2) to regional scale. This article describes and evaluates the trajectory model for Aerosol Dynamics, gas and particle phase CHEMistry and radiative transfer (ADCHEM). The model treats both vertical and horizontal dispersion perpendicular to an air mass trajectory (2-space dimensions). The Lagrangian approach enables a more detailed representation of the aerosol dynamics, gas and particle phase chemistry and a finer spatial and temporal resolution compared to that of available regional 3D-CTMs. These features make it among others well suited for urban plume studies. The aerosol dynamics model includes Brownian coagulation, dry deposition, wet deposition, in-cloud processing, condensation, evaporation, primary particle emissions and homogeneous nucleation. The organic mass partitioning was either modeled with a 2-dimensional volatility basis set (2D-VBS) or with the traditional two-product model approach. In ADCHEM these models consider the diffusion limited and particle size dependent condensation and evaporation of 110 and 40 different organic compounds respectively. The gas phase chemistry model calculates the gas phase concentrations of 61 different species, using 130 different chemical reactions. Daily isoprene and monoterpene emissions from European forests were simulated separately with the vegetation model LPJ-GUESS, and included as input to ADCHEM. ADCHEM was used to simulate the ageing of the urban plumes from the city of Malmö in southern Sweden (280 000 inhabitants). Several sensitivity tests were performed concerning the number of size bins, size structure method, aerosol dynamic processes, vertical and horizontal mixing, coupled or uncoupled condensation and the secondary organic aerosol formation. The simulations show that the full-stationary size structure gives accurate results with little numerical diffusion when more than 50 size bins are used between 1.5 and 2500 nm, while the moving-center method is preferable when only a few size bins are selected. The particle number size distribution in the center of the urban plume from Malmö was mainly affected by dry deposition, coagulation and vertical dilution. The modeled PM2.5 mass was dominated by organic material, nitrate, sulfate and ammonium. If the condensation of HNO3 and NH3 was treated as a coupled process (pH independent) the model gave lower nitrate PM2.5 mass than if considering uncoupled condensation. Although the time of ageing from that SOA precursors are emitted until condensable products are formed is substantially different with the 2D-VBS and two product model, the models gave similar total organic mass concentrations.

Roldin, P.; Swietlicki, E.; Schurgers, G.; Arneth, A.; Lehtinen, K. E. J.; Boy, M.; Kulmala, M.

2011-06-01

127

Development and evaluation of the aerosol dynamic and gas phase chemistry model ADCHEM  

NASA Astrophysics Data System (ADS)

The aim of this work was to develop a model ideally suited for detailed studies on aerosol dynamics, gas and particle phase chemistry within urban plumes, from local scale (1×1 km2) to regional or global scale. This article describes and evaluates the trajectory model for Aerosol Dynamics, gas and particle phase CHEMistry and radiative transfer (ADCHEM), which has been developed and used at Lund University since 2007. The model treats both vertical and horizontal dispersion perpendicular to an air mass trajectory (2-space dimensions), which is not treated in Lagrangian box-models (0-space dimensions). The Lagrangian approach enables a more detailed representation of the aerosol dynamics, gas and particle phase chemistry and a finer spatial and temporal resolution compared to that of available regional 3D-CTMs. These features make it among others ideally suited for urban plume studies. The aerosol dynamics model includes Brownian coagulation, dry deposition, wet deposition, in-cloud processing, condensation, evaporation, primary particle emissions and homogeneous nucleation. The gas phase chemistry model calculates the gas phase concentrations of 63 different species, using 119 different chemical reactions. Daily isoprene and monoterpene emissions from European forests were simulated separately with the vegetation model LPJ-GUESS, and included as input to ADCHEM. ADCHEM was used to simulate the ageing of the urban plumes from the city of Malmö in Southern Sweden (280 000 inhabitants). Several sensitivity tests were performed concerning the number of size bins, size structure method, coupled or uncoupled condensation, the volatility basis set (VBS) or traditional 2-product model for secondary organic aerosol formation, different aerosol dynamic processes and vertical and horizontal mixing. The simulations show that the full-stationary size structure gives accurate results with little numerical diffusion when more than 50 size bins are used between 1.5 and 2500 nm, while the moving-center method is preferable when only a few size bins are selected. The particle number size distribution in the center of the urban plume from Malmö is mainly affected by dry deposition, coagulation and condensation, and is relatively insensitive to moderate variations in the vertical and horizontal mixing, as long as the mixing height is relatively uniform. The modeled PM2.5 was dominated by organics, nitrate, sulfate and ammonium. If treating the condensation of HNO3 and NH3 as a coupled process (pH independent) the model gave lower nitrate PM2.5 values than if considering uncoupled condensation. However, both methods gave similar and significant temporal variation in the particulate nitrate content, primarily due to fluctuation in the relative humidity.

Roldin, P.; Swietlicki, E.; Schurgers, G.; Arneth, A.; Lehtinen, K. E. J.; Boy, M.; Kulmala, M.

2010-08-01

128

SVOC partitioning between the gas phase and settled dust indoors  

NASA Astrophysics Data System (ADS)

Semivolatile organic compounds (SVOCs) are a major class of indoor pollutants. Understanding SVOC partitioning between the gas phase and settled dust is important for characterizing the fate of these species indoors and the pathways by which humans are exposed to them. Such knowledge also helps in crafting measurement programs for epidemiological studies designed to probe potential associations between exposure to these compounds and adverse health effects. In this paper, we analyze published data from nineteen studies that cumulatively report measurements of dustborne and airborne SVOCs in more than a thousand buildings, mostly residences, in seven countries. In aggregate, measured median data are reported in these studies for 66 different SVOCs whose octanol-air partition coefficients ( Koa) span more than five orders of magnitude. We use these data to test a simple equilibrium model for estimating the partitioning of an SVOC between the gas phase and settled dust indoors. The results demonstrate, in central tendency, that a compound's octanol-air partition coefficient is a strong predictor of its abundance in settled dust relative to its gas phase concentration. Using median measured results for each SVOC in each study, dustborne mass fractions predicted using Koa and gas-phase concentrations correlate reasonably well with measured dustborne mass fractions ( R2 = 0.76). Combined with theoretical understanding of SVOC partitioning kinetics, the empirical evidence also suggests that for SVOCs with high Koa values, the mass fraction in settled dust may not have sufficient time to equilibrate with the gas phase concentration.

Weschler, Charles J.; Nazaroff, William W.

2010-09-01

129

Condensed phase rare gas halide exciplex lasers  

Microsoft Academic Search

XeF-doped solid argon constitutes the first solid state exciplex laser in which lasing action over the B to X, C to A, and D to X bands have been demonstrated. The results of these studies are summarized. Generalization of principles to other members of the large family of condensed phase exciplexes is considered. Ternary X:Rg:Rg-prime solids in which the diatomic

V. A. Apkarian

1990-01-01

130

Collision-induced gas phase dissociation rates  

NASA Technical Reports Server (NTRS)

The Landau-Zener theory of reactive cross sections was applied to diatomic molecules dissociating from a ladder of vibrational states. The result predicts a dissociation rate that is quite well duplicated by an Arrhenius function having a preexponential temperature dependence of about T(sub -1/2), at least for inert collision partners. This relation fits experimental data reasonably well. The theory is then used to calculate the effect of vibrational nonequilibrium on dissociation rate. For Morse oscillators, the results are about the same as given by Hammerling, Kivel, and Teare in their analytic approximation for harmonic oscillators, though at very high temperature a correction for the partition function limit is included. The empirical correction for vibration nonequilibrium proposed by Park, which is a convenient algorithm for CFD calculations, is modified to prevent a drastic underestimation of dissociation rates that occurs with this method when vibrational temperature is much smaller than the kinetic temperature of the gas.

Hansen, C. Frederick

1990-01-01

131

Freeze drying for gas chromatography stationary phase deposition  

SciTech Connect

The present disclosure relates to methods for deposition of gas chromatography (GC) stationary phases into chromatography columns, for example gas chromatography columns. A chromatographic medium is dissolved or suspended in a solvent to form a composition. The composition may be inserted into a chromatographic column. Alternatively, portions of the chromatographic column may be exposed or filled with the composition. The composition is permitted to solidify, and at least a portion of the solvent is removed by vacuum sublimation.

Sylwester, Alan P. (Livermore, CA)

2007-01-02

132

Analysis of the gas phase reactivity of chlorosilanes.  

PubMed

Trichlorosilane is the most used precursor to deposit silicon for photovoltaic applications. Despite of this, its gas phase and surface kinetics have not yet been completely understood. In the present work, it is reported a systematic investigation aimed at determining what is the dominant gas phase chemistry active during the chemical vapor deposition of Si from trichlorosilane. The gas phase mechanism was developed calculating the rate constant of each reaction using conventional transition state theory in the rigid rotor-harmonic oscillator approximation. Torsional vibrations were described using a hindered rotor model. Structures and vibrational frequencies of reactants and transition states were determined at the B3LYP/6-31+G(d,p) level, while potential energy surfaces and activation energies were computed at the CCSD(T) level using aug-cc-pVDZ and aug-cc-pVTZ basis sets extrapolating to the complete basis set limit. As gas phase and surface reactivities are mutually interlinked, simulations were performed using a microkinetic surface mechanism. It was found that the gas phase reactivity follows two different routes. The disilane mechanism, in which the formation of disilanes as reaction intermediates favors the conversion between the most stable monosilane species, and the radical pathway, initiated by the decomposition of Si2HCl5 and followed by a series of fast propagation reactions. Though both mechanisms are active during deposition, the simulations revealed that above a certain temperature and conversion threshold the radical mechanism provides a faster route for the conversion of SiHCl3 into SiCl4, a reaction that favors the overall Si deposition process as it is associated with the consumption of HCl, a fast etchant of Si. Also, this study shows that the formation of disilanes as reactant intermediates promotes significantly the gas phase reactivity, as they contribute both to the initiation of radical chain mechanisms and provide a catalytic route for the conversion between the most stable monosilanes. PMID:23731215

Ravasio, Stefano; Masi, Maurizio; Cavallotti, Carlo

2013-06-27

133

Gas purification in the dense phase at the CATS terminal  

SciTech Connect

The purification and transportation of natural gas at very high pressures can help to minimize the capital cost of pipelines and processing equipment. However, complex mixtures of hydrocarbons undergo unusual phase changes, such as retrograde condensation, as the temperature and pressure are altered. The Central Area Transmission System (CATS) is a joint venture of Amoci, BG, Amerada Hess, Phillips, Agip and Fina operated by Amoco on behalf of the owners. The design of the CATS terminal has provided an interesting processing challenge. The terminal receives a total of 1.6 Bscf/d of rich gas from a number of offshore fields. All are relatively sweet but the small amounts of H{sub 2}S and Hg are removed. Fixed bed technology was selected as the most economic purification process, while minimizing hydrocarbon loss and operator involvement. Conventionally, the raw gas would be split into the different hydrocarbon fractions and each would be processed separately. This would require the installation of a large number of reactors. A more elegant solution is to treat the gas on arrival at the terminal in the dense phase. This option raised questions around whether a fixed bed would be prone to fouling, could the pressure drop be kept low enough to avoid phase separation and would inadvertent wetting by condensation cause problems. Details are given of the test work carried out to prove the viability of using fixed bed technology for dense phase gas processing, the eventual design adopted and the performance over the first year of service.

Openshaw, P.J.; Carnell, P.J.H.; Rhodes, E.F.

1999-07-01

134

Improvement and further development in CESM/CAM5: gas-phase chemistry and inorganic aerosol treatments  

NASA Astrophysics Data System (ADS)

Gas-phase chemistry and subsequent gas-to-particle conversion processes such as new particle formation, condensation, and thermodynamic partitioning have large impacts on air quality, climate, and public health through influencing the amounts and distributions of gaseous precursors and secondary aerosols. Their roles in global air quality and climate are examined in this work using the Community Earth System Model version 1.0.5 (CESM1.0.5) with the Community Atmosphere Model version 5.1 (CAM5.1) (referred to as CESM1.0.5/CAM5.1). CAM5.1 includes a simple chemistry that is coupled with a 7-mode prognostic Modal Aerosol Model (MAM7). MAM7 includes classical homogenous nucleation (binary and ternary) and activation nucleation (empirical first-order power law) parameterizations, and a highly simplified inorganic aerosol thermodynamics treatment that only simulates particulate-phase sulfate and ammonium. In this work, a new gas-phase chemistry mechanism based on the 2005 Carbon Bond Mechanism for Global Extension (CB05_GE) and several advanced inorganic aerosol treatments for condensation of volatile species, ion-mediated nucleation (IMN), and explicit inorganic aerosol thermodynamics for sulfate, ammonium, nitrate, sodium, and chloride have been incorporated into CESM/CAM5.1-MAM7. Compared to the simple gas-phase chemistry, CB05_GE can predict many more gaseous species, and thus could improve model performance for PM2.5, PM10, PM components, and some PM gaseous precursors such as SO2 and NH3 in several regions as well as aerosol optical depth (AOD) and cloud properties (e.g., cloud fraction (CF), cloud droplet number concentration (CDNC), and shortwave cloud forcing, SWCF) on the global scale. The modified condensation and aqueous-phase chemistry could further improve the prediction of additional variables such as HNO3, NO2, and O3 in some regions, and new particle formation rate (J) and AOD on the global scale. IMN can improve the prediction of secondary PM2.5 components, PM2.5, and PM10 over Europe as well as AOD and CDNC on the global scale. The explicit inorganic aerosol thermodynamics using the ISORROPIA II model improves the prediction of all major PM2.5 components and their gaseous precursors in some regions as well as downwelling shortwave radiation, SWCF, and cloud condensation nuclei at a supersaturation of 0.5% on the global scale. For simulations of 2001-2005 with all the modified and new treatments, the improved model predicts that on global average, SWCF increases by 2.7 W m-2, reducing the normalized mean bias (NMB) of SWCF from -5.4 to 1.2%. Uncertainties in emissions can largely explain the inaccurate prediction of precursor gases (e.g., SO2, NH3, and NO) and primary aerosols (e.g., black carbon and primary organic matter). Additional factors leading to the discrepancies between model predictions and observations include assumptions associated with equilibrium partitioning for fine particles assumed in ISORROPIA II, irreversible gas/particle mass transfer treatment for coarse particles, uncertainties in model treatments such as dust emissions, secondary organic aerosol formation, multi-phase chemistry, cloud microphysics, aerosol-cloud interaction, dry and wet deposition, and model parameters (e.g., accommodation coefficients and prefactors of the nucleation power law) as well as uncertainties in model configuration such as the use of a coarse-grid resolution.

He, J.; Zhang, Y.

2014-09-01

135

Decay Pathways of Pyrimidine Bases: From Gas Phase to Solution  

Microsoft Academic Search

We use a variation of the pump-probe technique to unravel the photodynamics of nucleic acid bases and their water complexes.\\u000a Our work aims at bridging studies from the gas phase with those in the solution phase. Our results indicate that the intrinsic\\u000a properties of the pyrimidine bases can be dramatically modified by the surrounding environment. As isolated species, the bases

Wei Kong; Yonggang He; Chengyin Wu

136

Gas Phase Model of Surface Reactions for N{2} Afterglows  

NASA Astrophysics Data System (ADS)

The adequacy of the homogeneous gas phase model as a representation of the surface losses of diffusing active particles in gas phase is studied. As an example the recent data obtained for the surface recombination coefficients are reanalyzed. The data were obtained by the application of the breakdown delay times which consists of the measurements of the breakdown delay times t_d as a function of the afterglow period tau. It was found that for the conditions of our experiment, the diffusion should not be neglected as the final results are significantly different when obtained by approximate gas phase representation and by exact numerical solution to the diffusion equation. While application of the gas phase effective coefficients to represent surface losses gives an error in the value of the recombination coefficient, it reproduces correctly other characteristics such as order of the process which can be obtained from simple fits to the experimental data. Dans cet article, nous étudions la validité du modèle approximatif représentant les pertes superficielles des particules actives qui diffusent de la phase gazeuse comme pertes dans la phase homogène du gaz. Les données actuelles du coefficient de recombination en surface sont utilisées par cette vérification . Les données experimentales sont obtenues en utilisant la technique qui consiste en la mesure du temps de retard du début de la décharge en fonction de la période de relaxation. Nous avons trouvé que, pour nos conditions expérimentales, la diffusion ne peut être négligée. Aussi, les résultats finals sont considérablement différents quand ils sont obtenus en utilisant le modèle approximatif par comparaison aves les résultats obtenus par la solution numérique exacte de l'équation de la diffusion. L'application des coefficients effectifs dans la phase gaseuse pour la présentation des pertes superficielles donne, pour les coefficients de la recombinaison, des valeurs qui diffèrent en ordre de grandeur mais la méthode donne également correctement les autres caractéristiques ; par exemple l'ordre des processus en traçant simplement la courbe des données expérimentales.

Markovi?, V. Lj.; Petrovi?, Z. Lj.; Pejovi?, M. M.

1996-07-01

137

Gas-phase silicon micromachining with xenon difluoride  

Microsoft Academic Search

Xenon difluoride is a gas phase, room temperature, isotropic silicon etchant with extremely high selectivity to many materials commonly used in microelectromechancial systems, including photoresists, aluminum, and silicon dioxide. Using a simple vacuum system, the effects of etch aperture and loading were explored for etches between 10 and 200 micrometers . Etch rates as high as 40 micrometers \\/minute were

Floy I. Chang; Richard Yeh; Gisela Lin; Patrick B. Chu; Eric G. Hoffman; Ezekiel J. Kruglick; Kristofer S. Pister; Michael H. Hecht

1995-01-01

138

First measurements of gas phase sulphuric acid in the stratosphere  

Microsoft Academic Search

Measurements of the abundance of gas phase sulfuric acid in the stratosphere are reported. Compositions and abundances of stratospheric negative ions were observed at an altitude of 36.5 km, and the presence of species containing sulfuric acid molecules attached to HSO4(-) core ions was detected. A proposed reaction scheme suggests that the cores of these ions are formed by reactions

F. Arnold; R. Fabian

1980-01-01

139

Optically based diagnostics for gas-phase laser development  

Microsoft Academic Search

In this paper we describe several diagnostics that we have developed to assist the development of high power gas phase lasers including COIL, EOIL, and DPAL. For COIL we discuss systems that provide sensitive measurements of O2(a), small signal gain, iodine dissociation, and temperature. These are key operational parameters within COIL, and these diagnostics have been used world-wide to gain

Wilson T. Rawlins; Seonkyung Lee; Kristin L. Galbally-Kinney; William J. Kessler; Adam J. Hicks; Ian M. Konen; Emily P. Plumb; Steven J. Davis

2010-01-01

140

Thermal transformations of divinyl sulfone in the gas phase  

Microsoft Academic Search

The main products of the gas-phase pyrolysis (580–600°) of divinyl sulfone are SO2, acetylene, and ethylene; butadiene, benzene, toluene, isomeric xylenes, styrene, and benzothiophene are also formed in smaller amounts. In an H2S atmosphere the pyrolysis of divinyl sulfone is apparently accompanied by a partial reduction of the latter to divinyl sulfoxide.

M. G. Voronkov; É. N. Deryagina; É. N. Sukhomazova; V. Yu. Vitkovskii; N. K. Gusarova; B. A. Trofimov

1983-01-01

141

Selected examples of gas-phase ion chemistry studies.  

PubMed

Gas-phase ion chemistry is an area in mass spectrometry that has received much research interest since the mid fifties of the last century. Although the focus of mass spectrometric research has shifted the last twenty years largely to life science studies, including proteomics, genomics and metabolomics, there are still several groups in the world active in gas-phase ion chemistry of both positive and negative ions, either unimolecularly and/or bimolecularly. In this tutorial lecture the formation and determination of tautomeric ion structures and intra-ionic catalyzed tautomerization in the gas phase will be discussed. In addition, an example of formation of different tautomeric structures in protic and aprotic solvents under electrospray ionization conditions will be given, as established by gas-phase infrared multiphoton dissociation spectroscopy. This will be followed by presenting an example of time-resolved MS/MS which enables to identify the structure of an ion, generated at a particular molecular ion lifetime. At the end of the lecture the power of ion mobility will be shown in elucidating the mechanism of epimerization of bis-Tröger bases having chiral nitrogen centers. PMID:24349921

Nibbering, Nico M M

2013-01-01

142

Selected Examples of Gas-Phase Ion Chemistry Studies  

PubMed Central

Gas-phase ion chemistry is an area in mass spectrometry that has received much research interest since the mid fifties of the last century. Although the focus of mass spectrometric research has shifted the last twenty years largely to life science studies, including proteomics, genomics and metabolomics, there are still several groups in the world active in gas-phase ion chemistry of both positive and negative ions, either unimolecularly and/or bimolecularly. In this tutorial lecture the formation and determination of tautomeric ion structures and intra-ionic catalyzed tautomerization in the gas phase will be discussed. In addition, an example of formation of different tautomeric structures in protic and aprotic solvents under electrospray ionization conditions will be given, as established by gas-phase infrared multiphoton dissociation spectroscopy. This will be followed by presenting an example of time-resolved MS/MS which enables to identify the structure of an ion, generated at a particular molecular ion lifetime. At the end of the lecture the power of ion mobility will be shown in elucidating the mechanism of epimerization of bis-Tröger bases having chiral nitrogen centers. PMID:24349921

Nibbering, Nico M. M.

2013-01-01

143

Mass transfer between a multicomponent trapped gas phase and a mobile water phase: Experiment and theory  

NASA Astrophysics Data System (ADS)

Gas tracer experiments were carried out in dynamically compressed sediments to investigate the mass transfer between a trapped multicomponent gas phase and a mobile water phase. The saturation state of the column was characterized by three independent methods: (1) by gravimetric measurements, (2) by bromide tracer tests, and (3) by hydraulic conductivity measurements. For inverse modeling a new kinetic model was developed allowing volume change of the entrapped gas. The new kinetic model consistently explains oxygen elution curves, the time evolution of the integral gas saturation, and integral hydraulic conductivity. The sensitivity of three different velocity-dependent mass transfer correlations to the dissolution process was investigated: (1) a classical square-root, single-sphere correlation, Sh ˜ Pe0.5, (2) a multisphere correlation, Sh ˜ Pen (n = 0.5-1.0), and (3) an empirical correlation, Sh ˜ Pe0.8. It was found that all correlations yield nearly the same elution curves for 10 gas tracer experiments with three different two-component gas phases: O2/He, O2/N2, and O2/Ar and for different flow velocities ranging from 5 to 20 m d-1. For all gas tracer experiments a distinct minimum of the longitudinal dispersivity was found during gas dissolution, i.e., in the unsaturated state. For the saturated state we found that the experimental values could be described by Saffman's theory: ?p ? Pe ln (Pe) with a normalized mean square root error of 6%.

Geistlinger, Helmut; Beckmann, Annika; Lazik, Detlef

2005-11-01

144

Flavin adenine dinucleotide structural motifs: from solution to gas phase.  

PubMed

Flavin adenine dinucleotide (FAD) is involved in important metabolic reactions where the biological function is intrinsically related to changes in conformation. In the present work, FAD conformational changes were studied in solution and in gas phase by measuring the fluorescence decay time and ion-neutral collision cross sections (CCS, in a trapped ion mobility spectrometer, TIMS) as a function of the solvent conditions (i.e., organic content) and gas-phase collisional partner (i.e., N2 doped with organic molecules). Changes in the fluorescence decay suggest that FAD can exist in four conformations in solution, where the abundance of the extended conformations increases with the organic content. TIMS-MS experiments showed that FAD can exist in the gas phase as deprotonated (M = C27H31N9O15P2) and protonated forms (M = C27H33N9O15P2) and that multiple conformations (up to 12) can be observed as a function of the starting solution for the [M + H](+) and [M + Na](+)molecular ions. In addition, changes in the relative abundances of the gas-phase structures were observed from a "stack" to a "close" conformation when organic molecules were introduced in the TIMS cell as collision partners. Candidate structures optimized at the DFT/B3LYP/6-31G(d,p) were proposed for each IMS band, and results showed that the most abundant IMS band corresponds to the most stable candidate structure. Solution and gas-phase experiments suggest that the driving force that stabilizes the different conformations is based on the interaction of the adenine and isoalloxazine rings that can be tailored by the "solvation" effect created with the organic molecules. PMID:25222439

Molano-Arevalo, Juan Camilo; Hernandez, Diana R; Gonzalez, Walter G; Miksovska, Jaroslava; Ridgeway, Mark E; Park, Melvin A; Fernandez-Lima, Francisco

2014-10-21

145

Gas Phase Reactivity of Carboxylates with N-Hydroxysuccinimide Esters  

NASA Astrophysics Data System (ADS)

N-hydroxysuccinimide (NHS) esters have been used for gas-phase conjugation reactions with peptides at nucleophilic sites, such as primary amines (N-terminus, ?-amine of lysine) or guanidines, by forming amide bonds through a nucleophilic attack on the carbonyl carbon. The carboxylate has recently been found to also be a reactive nucleophile capable of initiating a similar nucleophilic attack to form a labile anhydride bond. The fragile bond is easily cleaved, resulting in an oxygen transfer from the carboxylate-containing species to the reagent, nominally observed as a water transfer. This reactivity is shown for both peptides and non-peptidic species. Reagents isotopically labeled with O18 were used to confirm reactivity. This constitutes an example of distinct differences in reactivity of carboxylates between the gas phase, where they are shown to be reactive, and the solution phase, where they are not regarded as reactive with NHS esters.

Peng, Zhou; McGee, William M.; Bu, Jiexun; Barefoot, Nathan Z.; McLuckey, Scott A.

2015-01-01

146

Hydration of Gas-Phase Ions Formed by Electrospray Ionization  

PubMed Central

The hydration of gas-phase ions produced by electrospray ionization was investigated. Evidence that the hydrated ions are formed by two mechanisms is presented. First, solvent condensation during the expansion inside the electrospray source clearly occurs. Second, some solvent evaporation from more extensively solvated ions or droplets is apparent. To the extent that these highly solvated ions have solution-phase structures, then the final isolated gas-phase structure of the ion will be determined by the solvent evaporation process. This process was investigated for hydrated gramicidin S in a Fourier-transform mass spectrometer. Unimolecular dissociation rate constants of isolated gramicidin S ions with between 2 and 14 associated water molecules were measured. These rate constants increased from 16 to 230 s?1 with increasing hydration, with smaller values corresponding to magic numbers. PMID:10497808

Rodriguez-Cruz, Sandra E.; Klassen, John S.; Williams, Evan R.

2005-01-01

147

Measurement and speciation of gas phase peroxides in the atmosphere  

NASA Astrophysics Data System (ADS)

The utility of an improved gas phase sampler and a recently developed nonenzymatic measurement method for H2O2 and HOCH2OOH(HMHP) is demonstrated. The gas phase sampler is equipped with a surfaceless intake to alleviate heterogeneous loss of H2O2 in the sampling line. The nonenzymatic method employs the aqueous phase Fenton reaction for H2O2 measurement and is capable of speciation between H2O2 and HMHP, using a dual channel technique. By adding a third channel employing the well-established method of p-hydroxyphenylacetic acid and horseradish peroxidase for total peroxide measurement, it is possible to differentiate H2O2, HMHP, and other organic peroxides, if present. Preliminary data analysis indicates that the measured total peroxides range from 0.4 to about 6 ppbv, depending on meteorological conditions, and that organic peroxides, mostly HMHP, constitute between 20 and 80 percent of the total peroxides.

Lee, J. H.; Leahy, D. F.; Tang, I. N.; Newman, L.

1993-02-01

148

Field driven ferromagnetic phase nucleation and propagation from the domain boundaries in antiferromagnetically coupled perpendicular anisotropy films  

SciTech Connect

We investigate the reversal process in antiferromagnetically coupled [Co/Pt]{sub X-1}/{l_brace}Co/Ru/[Co/Pt]{sub X-1}{r_brace}{sub 16} multilayer films by combining magnetometry and Magnetic soft X-ray Transmission Microscopy (MXTM). After out-of-plane demagnetization, a stable one dimensional ferromagnetic (FM) stripe domain phase (tiger-tail phase) for a thick stack sample (X=7 is obtained), while metastable sharp antiferromagnetic (AF) domain walls are observed in the remanent state for a thinner stack sample (X=6). When applying an external magnetic field the sharp domain walls of the thinner stack sample transform at a certain threshold field into the FM stripe domain wall phase. We present magnetic energy calculations that reveal the underlying energetics driving the overall reversal mechanisms.

Hauet, Thomas; Gunther, Christian M.; Hovorka, Ondrej; Berger, Andreas; Im, Mi-Young; Fischer, Peter; Hellwig, Olav

2008-12-09

149

Nucleation and growth of chemical vapor deposited diamond films  

NASA Astrophysics Data System (ADS)

This research involves a study of the nucleation and growth processes during diamond chemical vapor deposition (CVD) via numerical modeling and simulations. Numerical models have been developed: (1) to examine the chemistry of the intermediate layer that forms at the interface between diamond and non-diamond substrate, (2) to understand the nucleation, size and structure of diamond phase carbon clusters on Si(111) substrates, (3) to study the morphological instabilities associated with diamond growth during chemical vapor deposition. The chemistry of the intermediate layer that develops at the interface between diamond and non-diamond substrate during chemical vapor deposition is analyzed using a thermodynamic quasiequilibrium model. Substrates of Si, Mo, W, Ti, Ta, Fe and Ni are examined, and operating parameters such as the substrate temperature, reactor pressure, and CHsb4:Hsb2 ratio in the gas phase required for the growth of the respective metal carbides/solid carbon are predicted. It is shown that the quasiequilibrium approach is advantageous in that it minimizes the use of kinetics to the degree that rate expressions are obtained without requiring the knowledge of the detailed kinetic models of the processes. A theoretical study of the nucleation, size, and structure of diamond-phase carbon clusters on Si(111) substrates is presented. Silicon is chosen as the non-diamond substrate in this work as it is a common substrate material for diamond deposition. Molecular mechanics analysis has been utilized to predict energetically and entropically feasible pathways for nucleation of carbon clusters. Several mechanistic pathways for nucleation of carbon clusters are examined with Csb2Hsb2 and/or CHsb3 as the nucleation precursors. A possible model for the nucleation mechanism of diamond-phase carbon clusters on beta-SiC(111) surface, which forms epitaxially on Si(111) substrates, is presented. The critical size of the carbon clusters is calculated based on the atomistic theory of nucleation and the proposed nucleation mechanisms. The diamond CVD process has been examined theoretically and the morphological instabilities associated with the growth of diamond films have been investigated with a model based on the continuum species conservation equations coupled to surface reaction kinetics. An analytical model is developed to study the morphological instabilities of the diamond-gas interface during the diamond CVD process based on the linear and nonlinear perturbation theories. Linear stability analysis cannot be used to analyze the evolution of the unstable planar interface to a nonplanar cellular interface. Nonlinear analysis is carried out to study the growth behavior of an interface more accurately over a longer period of time. A two-dimensional numerical model describes the evolution of the gas-solid interface. The numerical and analytical models determine the critical parameters affecting the diamond deposition layer morphology. A dispersive relation is derived which relates the effects of species diffusive transport towards the growing interface, surface diffusion, surface tension, and geometrical factors with the stability of perturbations on the interface. (Abstract shortened by UMI.)

Mahalingam, Pushpa

150

Molecular dynamics simulations of the homogeneous nucleation of UF6 and SF6 molecules: Effects of the intramolecular vibrational relaxations on the nucleation rates  

NASA Astrophysics Data System (ADS)

The effects of flexibility in the homogeneous nucleation processes of UF6 and SF6 molecules from vapor phase were investigated by classical molecular dynamics (MD) simulations. We performed MD simulations using a flexible-molecule model and compared the results with those obtained from a rigid-molecule model. We took into account the flexibility of molecules in MD simulations by a harmonic intramolecular potential. We found that the nucleation rate in the flexible model of the UF6 molecule was about twice as large as that in the rigid model of UF6. This acceleration in nucleation rate was attributed to the flow of the condensation heat into the intramolecular vibrations. On the other hand, the nucleation rates in rigid and flexible models of SF6 were almost the same because the flow of the condensation heat into the intramolecular vibrations in the flexible model of SF6 was negligibly small. In order to confirm the reliability of the classical intramolecular vibrational model in the present work, we estimated the intramolecular vibrational relaxation times of the flexible UF6 and the flexible SF6 molecules in the gas phase using the same MD simulation technique as used for the nucleations. The intramolecular vibrational relaxation times obtained from the MD simulations were in good agreement with those from the experimental data in cases of both UF6 and SF6 molecules.

Tanimura, Shinobu; Yasuoka, Kenji; Ebisuzaki, Toshikazu

1998-09-01

151

Preconceptual design of the gas-phase decontamination demonstration cart  

SciTech Connect

Removal of uranium deposits from the interior surfaces of gaseous diffusion equipment will be a major portion of the overall multibillion dollar effort to decontaminate and decommission the gaseous diffusion plants. Long-term low-temperature (LTLT) gas-phase decontamination is being developed at the K-25 Site as an in situ decontamination process that is expected to significantly lower the decontamination costs, reduce worker exposure to radioactive materials, and reduce safeguard concerns. This report documents the preconceptual design of the process equipment that is necessary to conduct a full-scale demonstration of the LTLT method in accordance with the process steps listed above. The process equipment and method proposed in this report are not intended to represent a full-scale production campaign design and operation, since the gas evacuation, gas charging, and off-gas handling systems that would be cost effective in a production campaign are not cost effective for a first-time demonstration. However, the design presented here is expected to be applicable to special decontamination projects beyond the demonstration, which could include the Deposit Recovery Program. The equipment will therefore be sized to a 200 ft size 1 converter (plus a substantial conservative design margin), which is the largest item of interest for gas phase decontamination in the Deposit Recovery Program. The decontamination equipment will allow recovery of the UF{sub 6}, which is generated from the reaction of ClF{sub 3} with the uranium deposits, by use of NaF traps.

Munday, E.B.

1993-12-01

152

Improved coarse-grained model for molecular-dynamics simulations of water nucleation  

NASA Astrophysics Data System (ADS)

We developed a new coarse-grained (CG) model for water to study nucleation of droplets from the vapor phase. The resulting potential has a more flexible functional form and a longer range cutoff compared to other CG potentials available for water. This allowed us to extend the range of applicability of coarse-grained techniques to nucleation phenomena. By improving the description of the interactions between water molecules in the gas phase, we obtained CG model that gives similar results than the all-atom (AA) TIP4P model but at a lower computational cost. In this work we present the validation of the potential and its application to the study of nucleation of water droplets from the supersaturated vapor phase via molecular-dynamics simulations. The computed nucleation rates at T = 320 K and 350 K at different supersaturations, ranging from 5 to 15, compare very well with AA TIP4P simulations and show the right dependence on the temperature compared with available experimental data. To help comparison with the experiments, we explored in detail the different ways to control the temperature and the effects on nucleation.

Zipoli, Federico; Laino, Teodoro; Stolz, Steffen; Martin, Elyette; Winkelmann, Christoph; Curioni, Alessandro

2013-09-01

153

Carbon Dioxide Separation from Flue Gas by Phase Enhanced Absorption  

SciTech Connect

A new process, phase enhanced absorption, was invented. The method is carried out in an absorber, where a liquid carrier (aqueous solution), an organic mixture (or organic compound), and a gas mixture containing a gas to be absorbed are introduced from an inlet. Since the organic mixture is immiscible or at least partially immiscible with the liquid carrier, the organic mixture forms a layer or small parcels between the liquid carrier and the gas mixture. The organic mixture in the absorber improves mass transfer efficiency of the system and increases the absorption rate of the gas. The organic mixture serves as a transportation media. The gas is finally accumulated in the liquid carrier as in a conventional gas-liquid absorption system. The presence of the organic layer does not hinder the regeneration of the liquid carrier or recovery of the gas because the organic layer is removed by a settler after the absorption process is completed. In another aspect, the system exhibited increased gas-liquid separation efficiency, thereby reducing the costs of operation and maintenance. Our study focused on the search of the organic layer or transportation layer to enhance the absorption rate of carbon dioxide. The following systems were studied, (1) CO{sub 2}-water system and CO{sub 2}-water-organic layer system; (2) CO{sub 2}-Potassium Carbonate aqueous solution system and CO{sub 2}-Potassium Carbonate aqueous solution-organic layer system. CO{sub 2}-water and CO{sub 2}-Potassium Carbonate systems are the traditional gas-liquid absorption processes. The CO{sub 2}-water-organic layer and CO{sub 2}-Potassium Carbonate-organic layer systems are the novel absorption processes, phase enhanced absorption. As we mentioned early, organic layer (transportation layer phase) is used for the increase of absorption rate. Our study showed that the absorption rate can be increased by adding the organic layer. However, the enhanced factor is highly depended on the liquid mass transfer coefficient.

Liang Hu

2006-06-30

154

Effect of Be on the nucleation and growth of beta' phase in aluminum-magnesium-silicon alloy  

Microsoft Academic Search

An investigation on the effect of Be on betasp' phase precipitation in Al-0.7%Mg-0.4%Si alloy was carried out using microhardness and resistivity measurements, and optical and TEM observations. It is shown that addition of 0.4%Be to an Al-0.7%Mg-0.4%Si (base) alloy significantly enhances the age hardening response and increases the peak hardness levels of the alloy, which is associated with a refinement

Ali Hatab

1997-01-01

155

Efimov-driven phase transitions of the unitary Bose gas  

NASA Astrophysics Data System (ADS)

Initially predicted in nuclear physics, Efimov trimers are bound configurations of three quantum particles that fall apart when any one of them is removed. They open a window into a rich quantum world that has become the focus of intense experimental and theoretical research, as the region of ‘unitary’ interactions, where Efimov trimers form, is now accessible in cold-atom experiments. Here we use a path-integral Monte Carlo algorithm backed up by theoretical arguments to show that unitary bosons undergo a first-order phase transition from a normal gas to a superfluid Efimov liquid, bound by the same effects as Efimov trimers. A triple point separates these two phases and another superfluid phase, the conventional Bose-Einstein condensate, whose coexistence line with the Efimov liquid ends in a critical point. We discuss the prospects of observing the proposed phase transitions in cold-atom systems.

Piatecki, Swann; Krauth, Werner

2014-03-01

156

High-quality AlN growth on 6H-SiC substrate using three dimensional nucleation by low-pressure hydride vapor phase epitaxy  

NASA Astrophysics Data System (ADS)

There is a method of controlling nucleation and lateral growth using the three-dimensional (3D) and two-dimensional (2D) growth modes to reduce the dislocation density. We performed 3D-2D-AlN growth on 6H-SiC substrates to obtain high-quality and crack-free AlN layers by low-pressure hydride vapor phase epitaxy (LP-HVPE). First, we performed 3D-AlN growth directly on a 6H-SiC substrate. With increasing V/III ratio, the AlN island density decreased and the grain size increased. Second, 3D-2D-AlN layers were grown directly on a 6H-SiC substrate. With increasing the V/III ratio of 3D-AlN, the crystalline qualities of the 3D-2D-AlN layer were improved. Third, we performed 3D-2D-AlN growth on a trench-patterned 6H-SiC substrate. The crack density was reduced to relax the stress by voids. We also evaluated the threading dislocation density by using molten KOH/NaOH etching. As a result, the estimated edge dislocation density of the 3D-2D-AlN sample was 3.9 × 108 cm-2.

Kitagawa, Shin; Miyake, Hideto; Hiramatsu, Kazumasa

2014-01-01

157

Structure and Dynamics of Oligonucleotides in the Gas Phase.  

PubMed

By combining ion-mobility mass spectrometry experiments with sub-millisecond classical and ab initio molecular dynamics we fully characterized, for the first time, the dynamic ensemble of a model nucleic acid in the gas phase under electrospray ionization conditions. The studied oligonucleotide unfolds upon vaporization, loses memory of the solution structure, and explores true gas-phase conformational space. Contrary to our original expectations, the oligonucleotide shows very rich dynamics in three different timescales (multi-picosecond, nanosecond, and sub-millisecond). The shorter timescale dynamics has a quantum mechanical nature and leads to changes in the covalent structure, whereas the other two are of classical origin. Overall, this study suggests that a re-evaluation on our view of the physics of nucleic acids upon vaporization is needed. PMID:25417598

Arcella, Annalisa; Dreyer, Jens; Ippoliti, Emiliano; Ivani, Ivan; Portella, Guillem; Gabelica, Valérie; Carloni, Paolo; Orozco, Modesto

2014-11-21

158

Time of Nucleation of Phase-Slip Centers in YBa2Cu3O7 Superconducting Bridges  

NASA Astrophysics Data System (ADS)

Narrow YBa2Cu3O7 films, excited by pulses of supercritical current, had their nanosecond electric response monitored in zero applied magnetic field. Delayed voltage steps plus constant differential resistance, characteristic of phase-slip centers (PSC), are observed at all temperatures. The duration of the initial zero voltage state is well fit by Ginzburg-Landau based theories, with a gap relaxation time controlled by phonon escape. At higher levels of excitation, PSC's give birth to slowly spreading normal hot spots.

Jelila, F. S.; Maneval, J.-P.; Ladan, F.-R.; Chibane, F.; Marie-de-Ficquelmont, A.; Méchin, L.; Villégier, J.-C.; Aprili, M.; Lesueur, J.

1998-08-01

159

Photodissociation pathways of gas-phase photoactive yellow protein chromophores  

NASA Astrophysics Data System (ADS)

The absorption dynamics of two model chromophores of the photoactive yellow protein were studied in gas-phase experiments. Using different time-resolving techniques with an overall sensitivity ranging from seconds down to a few nanoseconds, complex dynamics were revealed for the p -coumaric acid anion, involving both fragmentation and electron detachment as possible photoresponse channels. For the trans-thiophenyl- p -coumarate model, despite its more complex molecular structure, simpler decay dynamics showing only fragmentation were observed.

Lammich, Lutz; Rajput, Jyoti; Andersen, Lars H.

2008-11-01

160

Gas phase fractionation method using porous ceramic membrane  

DOEpatents

Flaw-free porous ceramic membranes fabricated from metal sols and coated onto a porous support are advantageously used in gas phase fractionation methods. Mean pore diameters of less than 40 .ANG., preferably 5-20 .ANG. and most preferably about 15 .ANG., are permeable at lower pressures than existing membranes. Condensation of gases in small pores and non-Knudsen membrane transport mechanisms are employed to facilitate and increase membrane permeability and permselectivity.

Peterson, Reid A. (Madison, WI); Hill, Jr., Charles G. (Madison, WI); Anderson, Marc A. (Madison, WI)

1996-01-01

161

Scale up of gas-phase chlorination reactors using CFD  

Microsoft Academic Search

Gas-phase chlorination of methyl chloride is an important industrial process producing widely applied chlorinated derivatives. Control over reactor stability and product distribution necessitates a thorough study of the strongly coupled turbulent flow and reaction processes in chlorination reactors. In this work, a hybrid finite-volume (FV)\\/transported probability density function (PDF) method is employed to analyze the performance of a coaxial jet-stirred

Ying Liu; V. Raman; R. O. Fox; A. D. Harvey

2004-01-01

162

Experimental study of gas phase titanium and aluminum oxide clusters  

Microsoft Academic Search

We present an experimental study of the vibrational properties of gas phase titanium oxide and aluminum oxide clusters. The titanium and aluminum oxide clusters have a stoichiometry of (Ti2O3) x-(TiO2)y (with (x, y) from (2, 4) to (11, 29)) and AlO-(Al2O3)n (5 <= n <= 70). The vibrational properties of the clusters are obtained using infrared resonance enhanced multi-photon ionization

K. Demyk; D. van Heijnsbergen; G. von Helden; G. Meijer

2004-01-01

163

Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystals and Polytetrehedral-Phase-Forming Alloys  

NASA Technical Reports Server (NTRS)

By investigating the properties of quasicrystals and quasicrystal-forming liquid alloys, we may determine the role of ordering of the liquid phase in the formation of quasicrystals, leading to a better fundamental understanding of both the quasicrystal and the liquid. A quasicrystal is solid characterized by a symmetric but non-periodic arrangement of atoms, usually in the form of an icosahedron (12 atoms, 20 triangular faces). It is theorized that the short-range order in liquids takes this same form. The degree of ordering depends on the temperature of the liquid, and affects many of the liquid s properties, including specific heat, viscosity, and electrical resistivity. The MSFC role in this project includes solidification studies, phase diagram determination, and thermophysical property measurements on the liquid quasicrystal-forming alloys, all by electrostatic levitation (ESL). The viscosity of liquid quasicrystal-forming alloys is measured by the oscillating drop method, both in the stable and undercooled liquid state. The specific heat of solid, undercooled liquid, and stable liquid are measured by the radiative cooling rate of the droplets.

2003-01-01

164

Structure of triplex DNA in the gas phase.  

PubMed

Extensive (more than 90 microseconds) molecular dynamics simulations complemented with ion-mobility mass spectrometry experiments have been used to characterize the conformational ensemble of DNA triplexes in the gas phase. Our results suggest that the ensemble of DNA triplex structures in the gas phase is well-defined over the experimental time scale, with the three strands tightly bound, and for the most abundant charge states it samples conformations only slightly more compact than the solution structure. The degree of structural alteration is however very significant, mimicking that found in duplex and much larger than that suggested for G-quadruplexes. Our data strongly supports that the gas phase triplex maintains an excellent memory of the solution structure, well-preserved helicity, and a significant number of native contacts. Once again, a linear, flexible, and charged polymer as DNA surprises us for its ability to retain three-dimensional structure in the absence of solvent. Results argue against the generally assumed roles of the different physical interactions (solvent screening of phosphate repulsion, hydrophobic effect, and solvation of accessible polar groups) in modulating the stability of DNA structures. PMID:22420643

Arcella, Annalisa; Portella, Guillem; Ruiz, Maria Luz; Eritja, Ramon; Vilaseca, Marta; Gabelica, Valérie; Orozco, Modesto

2012-04-18

165

Carbon Dioxide Separation from Flue Gas by Phase Enhanced Absorption  

SciTech Connect

A new process, phase enhanced absorption, was invented. The method is carried out in an absorber, where a liquid carrier (aqueous solution), an organic mixture (or organic compound), and a gas mixture containing a gas to be absorbed are introduced from an inlet. Since the organic mixture is immiscible or at least partially immiscible with the liquid carrier, the organic mixture forms a layer or small parcels between the liquid carrier and the gas mixture. The organic mixture in the absorber improves mass transfer efficiency of the system and increases the absorption rate of the gas. The organic mixture serves as a transportation media. The gas is finally accumulated in the liquid carrier as in a conventional gas-liquid absorption system. The presence of the organic layer does not hinder the regeneration of the liquid carrier or recovery of the gas because the organic layer is removed by a settler after the absorption process is completed. In another aspect, the system exhibited increased gas-liquid separation efficiency, thereby reducing the costs of operation and maintenance. Our study focused on the search of the organic layer or transportation layer to enhance the absorption rate of carbon dioxide. The following systems were studied, (1) CO{sub 2}-water system and CO{sub 2}-water-organic layer system; (2) CO{sub 2}-Potassium Carbonate aqueous solution system and CO{sub 2}-Potassium Carbonate aqueous solution-organic layer system. CO{sub 2}-water and CO{sub 2}-Potassium Carbonate systems are the traditional gas-liquid absorption processes. The CO{sub 2}-water-organic layer and CO{sub 2}-Potassium Carbonate-organic layer systems are the novel absorption processes, phase enhanced absorption. As we mentioned early, organic layer is used for the increase of absorption rate, and plays the role of transportation of CO{sub 2}. Our study showed that the absorption rate can be increased by adding the organic layer. However, the enhanced factor is highly depended on the liquid mass transfer coefficients for the CO{sub 2}-water-organic layer system. For the CO{sub 2}-Potassium Carbonate aqueous solution-organic layer system, the enhanced factor is not only dependent on the liquid mass transfer coefficients, but also the chemical reaction rates.

Tim Fout

2007-06-30

166

Gas–liquid two-phase flow in microchannels Part I: two-phase flow patterns  

Microsoft Academic Search

Capillary gas–liquid two-phase flow occurs in increasingly more modern industrial applications. The existing relevant data are limited and are inconsistent with respect to the reported flow patterns and their transition boundaries. A systematic experimental investigation of two-phase flow patterns in microchannels was the objective of this study.Using air and water, experiments were conducted in circular microchannels with 1.1 and 1.45mm

K. A. Triplett; S. M. Ghiaasiaan; S. I. Abdel-Khalik; D. L. Sadowski

1999-01-01

167

GAS PHASE SELECTIVE PHOTOXIDATION OF ALCOHOLS USING LIGHT-ACTIVATED TITANIUM DIOXIDE AND MOLECULAR OXYGEN  

EPA Science Inventory

Gas Phase Selective Oxidation of Alcohols Using Light-Activated Titanium Dioxide and Molecular Oxygen Gas phase selective oxidations of various primary and secondary alcohols are studied in an indigenously built stainless steel up-flow photochemical reactor using ultravi...

168

The partitioning of ketones between the gas and aqueous phases  

NASA Astrophysics Data System (ADS)

Most ketones are not significantly hydrated; they therefore retain their chromophore and they could be photolytically degraded in solution yielding a variety of products including carboxylic acids, aldehydes and radicals. It is difficult to accurately model the partitioning of ketones between the gas phase and aqueous phase because of the lack suitable estimates of the Henry's Law constants; consequently the fate and environmental effects of ketones cannot be confidently predicted. Here we report the experimental determination of the Henry's Law constants of a series of ketones that has yielded a simple straight line equation to predict the Henry's Law constants of simple aliphatic ketones: log H ? =0.23?? ? + 1.51; where H ? is the effective Henry's Law constant (M atm -1, and ?? ? is the Taft polar substituents constants. The results for 25°C are (M atm -1) CH 3COCH 3, 32; C 6H 5COCH 3, 110; CH 2ClCOCH 3, 59; CH 3COCOCH 3, 74; CF 3COCH 3, 138. Acetophenone appears to have an abnormally high H ?. Most low molecular weight aliphatic ketones are predicted to characterized by H ??30 M atm -1 and therefore they are expected to be found in the aqueous phase at concentrations of ?5 - 0.5 ?M (given a typical gas-phase concentration range of 1-10 ppbv). The expected rate of decomposition of ketones due to photolysis in hydrometers is briefly discussed.

Betterton, Eric A.

169

Effect of gas-phase transport in molten carbonate fuel cell  

Microsoft Academic Search

Electrode reaction characteristics involving gas-phase transport effect have been investigated with several 100 cm2 class molten carbonate fuel cells (MCFCs). Although the MCFCs operate on gas-phase reactants at relatively high temperature, most of studies on the electrode reaction kinetics have been confined within kinetic-control and liquid-phase mass-transfer regions. To evaluate the gas-phase transport effect in the MCFC, an inert gas

Choong-Gon Lee; Byoung-Sam Kang; Hai-Kyung Seo; Hee-Chun Lim

2003-01-01

170

Revision of the thermodynamics of the proton in gas phase.  

PubMed

Proton transfer is ubiquitous in various physical/chemical processes, and the accurate determination of the thermodynamic parameters of the proton in the gas phase is useful for understanding and describing such reactions. However, the thermodynamic parameters of such a proton are usually determined by assuming the proton as a classical particle whatever the temperature. The reason for such an assumption is that the entropy of the quantum proton is not always soluble analytically at all temperatures. Thereby, we addressed this matter using a robust and reliable self-consistent iterative procedure based on the Fermi-Dirac formalism. As a result, the free proton gas can be assumed to be classical for temperatures higher than 200 K. However, it is worth mentioning that quantum effects on the gas phase proton motion are really significant at low temperatures (T ? 120 K). Although the proton behaves as a classical particle at high temperatures, we strongly recommend the use of quantum results at all temperatures, for the integrated heat capacity and the Gibbs free energy change. Therefore, on the basis of the thermochemical convention that ignores the proton spin, we recommend the following revised values for the integrated heat capacity and the Gibbs free energy change of the proton in gas phase and, at the standard pressure (1 bar): ?H0?T = 6.1398 kJ mol(-1) and ?G0?T = -26.3424 kJ mol(-1). Finally, it is important noting that the little change of the pressure from 1 bar to 1 atm affects notably the entropy and the Gibbs free energy change of the proton. PMID:25338234

Fifen, Jean Jules; Dhaouadi, Zoubeida; Nsangou, Mama

2014-11-20

171

Specific, trace gas induced phase transition in copper(II)oxide for highly selective gas sensing  

NASA Astrophysics Data System (ADS)

Here, we present results on the investigation of the percolation phase transition in copper(II)oxide (CuO) and show how it may be used to determine trace gas concentrations. This approach provides a highly selective sensing mechanism for the detection of hydrogen sulfide even in oxygen depleted atmospheres. In real-world applications, this scenario is encountered in biogas plants and natural gas facilities, where reliable H2S sensing and filtering are important because of the destructive effects H2S has on machinery. As opposed to gas detection via standard metal-oxide reaction routes, the percolation dynamics are demonstrated to be independent of the surface morphology in accordance with the universality of phase transitions. The sensing behavior of ink-jet printed CuO layers was tested for a large set of parameters including layer temperature, hydrogen sulfide (H2S) and oxygen concentration, as well as the sensitivity towards other gas species. The electrical percolation of the sensing layer is heralded by a dramatic drop in the overall resistivity of the CuO layer for temperatures below 200 °C. The observed percolation phenomena in this temperature regime are unique to H2S even in comparison with related volatile thio-compounds making the sensing mechanism highly selective. At elevated temperatures above 300 °C, the phase transition does not occur. This enables two distinct operational modes which are tunable via the sensor temperature and also allows for resetting the sensing layer after an electrical breakthrough.

Kneer, J.; Wöllenstein, J.; Palzer, S.

2014-08-01

172

Nucleation-induced transition to collective motion in active systems  

NASA Astrophysics Data System (ADS)

While the existence of polar ordered states in active systems is well established, the dynamics of the self-assembly processes are still elusive. We study a lattice gas model of self-propelled elongated particles interacting through excluded volume and alignment interactions, which shows a phase transition from an isotropic to a polar ordered state. By analyzing the ordering process we find that the transition is driven by the formation of a critical nucleation cluster and a subsequent coarsening process. Moreover, the time to establish a polar ordered state shows a power-law divergence.

Weber, Christoph A.; Schaller, Volker; Bausch, Andreas R.; Frey, Erwin

2012-09-01

173

Ice Nucleation in Deep Convection  

NASA Technical Reports Server (NTRS)

The processes controlling production of ice crystals in deep, rapidly ascending convective columns are poorly understood due to the difficulties involved with either modeling or in situ sampling of these violent clouds. A large number of ice crystals are no doubt generated when droplets freeze at about -40 C. However, at higher levels, these crystals are likely depleted due to precipitation and detrainment. As the ice surface area decreases, the relative humidity can increase well above ice saturation, resulting in bursts of ice nucleation. We will present simulations of these processes using a large-eddy simulation model with detailed microphysics. Size bins are included for aerosols, liquid droplets, ice crystals, and mixed-phase (ice/liquid) hydrometers. Microphysical processes simulated include droplet activation, freezing, melting, homogeneous freezing of sulfate aerosols, and heterogeneous ice nucleation. We are focusing on the importance of ice nucleation events in the upper part of the cloud at temperatures below -40 C. We will show that the ultimate evolution of the cloud in this region (and the anvil produced by the convection) is sensitive to these ice nucleation events, and hence to the composition of upper tropospheric aerosols that get entrained into the convective column.

Jensen, Eric; Ackerman, Andrew; Stevens, David; Gore, Warren J. (Technical Monitor)

2001-01-01

174

Propagation of acoustic waves in a viscoelastic two-phase system: influence of gas bubble concentration  

NASA Astrophysics Data System (ADS)

Volcanic explosions generate pressure perturbations in the atmosphere and a seismic wavefield in the ground. The source is therefore well coupled with the atmosphere and the ground. The acoustic and elastic wavefields reflect dynamical processes at the source and the viscoelastic properties of the magma-gas medium. At low pressure (<10 MPa), magma cannot be considered as a homogeneous medium, and must be treated as a mixture of fluid magma and gas bubbles. Acoustic waves are strongly affected by the transmission properties of the magma-gas medium. We analyze the propagation of the acoustic wavefield in a two-phase medium in which the viscosity and compressibility are spatially inhomogeneous. Gas bubble nucleation starts when the magma pressure drops below the supersaturation level (at a depth of a few hundred m for H 2O in basaltic magmas) and the gas-volume fraction increases toward the surface, reaching its maximum value at the magma-air interface. The variation of gas-volume fraction is non-linear with depth and is particularly strong at shallow depths (<50 m). Density and sound velocity of the mixture drop drastically and the shear viscosity of the mixture increases with decreasing depth. Under these conditions, we tested if the propagation of an acoustic wavefield generated by a source embedded in the magma column can generate an infrasonic wavefield in the atmosphere. The acoustic wavefield in the magma is here modeled as function of the void fraction in the magma and resonance is considered to be induced only by body-wave. Large gas bubble concentrations (>70%) strongly affect the propagation properties of the acoustic wavefield. We found that the amplitude of the infrasonic wavefield in the atmosphere typically recorded in case of strombolian explosions (2×10 5 Pa) can be explained by a deep (>50 m) source embedded in the magma conduit only if a very large unrealistic pressure drop (10 13 Pa) is assumed. The strong damping, linked to the poor elastic properties of the shallow magma-gas mixture, prevents the efficient propagation of the acoustic waves in the magma-gas mixture, and resonance of body waves cannot occur. Infrasonic waves can be transmitted from the magma to the atmosphere only when the source is very shallow (<10 m). In conclusion, we neglect the possibility that resonance of body waves can induce infrasonic waves in the atmosphere. Moreover, we introduce new evidence of a strong attenuation induced by the shear viscosity on the propagation of elastic waves in a gas-rich magma. We believe that this latter result could have also a large impact on all the theories based on the resonance of elastic waves in a conduit as model to explain tremor and/or LP events on volcanoes.

Marchetti, Emanuele; Ichihara, Mie; Ripepe, Maurizio

2004-09-01

175

Enantioselectivity in gas-phase ion-molecule reactions  

NASA Astrophysics Data System (ADS)

Comprehensive understanding of information transfer between chiral molecules in living systems and in supramolecular assemblies requires the quantitative determination of the intrinsic short-range forces controlling enantioselectivity in simplified models, such as diastereomeric ion-molecule complexes in the isolated state. This review article describes the state-of-art in this field. Emphasis is put on the generation of diastereomeric ion-molecule aggregates in the gas phase and the determination of their relative stability and reactivity by mass spectrometric and radiolytic techniques.

Speranza, Maurizio

2004-04-01

176

A multiwatt all gas-phase iodine laser (AGIL)  

NASA Astrophysics Data System (ADS)

The demonstration and characterization of a multiwatt All Gas-phase Iodine Laser (AGIL) are described. A 20-cm subsonic reactor was used to produce NCl(a1?) for a series parametric studies of the I*(2P1/2) - I(2P3/2) small signal gain and extracted power dependence on reactant flow rates and reaction time. A reduction in the flow channel height led to improved performance. The highest measured gain was 4.2 x 10-4 cm-1 and the highest power observed was 31 W.

Manke, Gerald C., II; Cooper, Chris B.; Dass, Shiv C.; Madden, Timothy J.; Hager, Gordon D.

2004-05-01

177

A multiwatt all gas-phase iodine laser (AGIL)  

NASA Astrophysics Data System (ADS)

The demonstration and characterization of a multiwatt All Gas-phase Iodine Laser (AGIL) are described. A 20-cm subsonic reactor was used to produce NCl(a1?) for a series parametric studies of the I*(2P1/2) - I(2P3/2) small signal gain and extracted power dependence on reactant flow rates and reaction time. A reduction in the flow channel height led to improved performance. The highest measured gain was 4.2 x 10-4 cm-1 and the highest power observed was 31 W.

Manke, Gerald C., II; Cooper, Chris B.; Dass, Shiv C.; Madden, Timothy J.; Hager, Gordon D.

2004-09-01

178

Mulitwatt all gas-phase iodine laser (AGIL)  

NASA Astrophysics Data System (ADS)

The demonstration and characterization of a multi-watt All Gas-phase Iodine Laser (AGIL) are described. A 20-cm subsonic reactor was used to produce NCl(a1?) for a series of parametric studies of the I*(2P1/2)-I(2P3/2) small signal gain and extracted power dependence on reactant flow rates and reaction time. The highest measured gain was 2.5x10-4 cm-1 and the highest power observed was 18 W.

Manke, Gerald C., II; Cooper, Chris B.; Dass, Shiv C.; Madden, Timothy J.; Hager, Gordon D.

2003-06-01

179

Multiscale Aspects of Modeling Gas-Phase Nanoparticle Synthesis  

PubMed Central

Aerosol reactors are utilized to manufacture nanoparticles in industrially relevant quantities. The development, understanding and scale-up of aerosol reactors can be facilitated with models and computer simulations. This review aims to provide an overview of recent developments of models and simulations and discuss their interconnection in a multiscale approach. A short introduction of the various aerosol reactor types and gas-phase particle dynamics is presented as a background for the later discussion of the models and simulations. Models are presented with decreasing time and length scales in sections on continuum, mesoscale, molecular dynamics and quantum mechanics models. PMID:23729992

Buesser, B.; Gröhn, A.J.

2013-01-01

180

Isotropic and anisotropic dipeptide films based on gas phase deposition  

NASA Astrophysics Data System (ADS)

We demonstrated the fabrication and application of well-ordered and vertically aligned dipeptide nanostructures based on a simple gas phase deposition. Deposited nanostructures exhibited the superhydrophobic property with a very low sliding angle. Highly reproducible SERS data have also been obtained after combining deposited films with a thin layer of gold. In addition to these, directional peptide films were, for the first time, successfully fabricated based on the oblique angle deposition technique. We believe that such bio-inspired materials would have a great impact in several technological applications involving catalysis, tissue engineering and biosensors.

Demirel, Gokhan; Tamer, Ugur

2012-06-01

181

Experiments on Nucleation in Different Flow Regimes  

NASA Technical Reports Server (NTRS)

The vast majority of metallic engineering materials are solidified from the liquid phase. Understanding the solidification process is essential to control microstructure, which in turn, determines the properties of materials. The genesis of solidification is nucleation, where the first stable solid forms from the liquid phase. Nucleation kinetics determine the degree of undercooling and phase selection. As such, it is important to understand nucleation phenomena in order to control solidification or glass formation in metals and alloys. Early experiments in nucleation kinetics were accomplished by droplet dispersion methods [1-6]. Dilitometry was used by Turnbull and others, and more recently differential thermal analysis and differential scanning calorimetry have been used for kinetic studies. These techniques have enjoyed success; however, there are difficulties with these experiments. Since materials are dispersed in a medium, the character of the emulsion/metal interface affects the nucleation behavior. Statistics are derived from the large number of particles observed in a single experiment, but dispersions have a finite size distribution which adds to the uncertainty of the kinetic determinations. Even though temperature can be controlled quite well before the onset of nucleation, the release of the latent heat of fusion during nucleation of particles complicates the assumption of isothermality during these experiments. Containerless processing has enabled another approach to the study of nucleation kinetics [7]. With levitation techniques it is possible to undercool one sample to nucleation repeatedly in a controlled manner, such that the statistics of the nucleation process can be derived from multiple experiments on a single sample. The authors have fully developed the analysis of nucleation experiments on single samples following the suggestions of Skripov [8]. The advantage of these experiments is that the samples are directly observable. The nucleation temperature can be measured by noncontact optical pyrometry, the mass of the sample is known, and post processing analysis can be conducted on the sample. The disadvantages are that temperature measurement must have exceptionally high precision, and it is not possible to isolate specific heterogeneous sites as in droplet dispersions.

Bayuzick, Robert J.

1999-01-01

182

Reynolds number dependence of gas-phase turbulence in gas–particle flows  

Microsoft Academic Search

A downward flow of glass bead particles in a vertical pipe is investigated using a two-component LDV\\/PDPA for a range of Re (6400gas-phase turbulence intensity at the lowest value

K. Hadinoto; E. N. Jones; C. Yurteri; J. S. Curtis

2005-01-01

183

Raman study of vibrational dynamics of aminopropylsilanetriol in gas phase.  

PubMed

Raman spectrum of aminopropylsilanetriol (APST) in gas phase has been recorded at room temperature in macro chamber utilizing two-mirror technique over the sample tube. Unlike predominantly trans molecular conformation in condensed phase, the spectra of vapor show that the molecules are solely in gauche conformation with intramolecular hydrogen bond N···HO which reduces the molecular energy in respect to trans conformation by 0.152 eV. The assignment of the molecular spectra based on the DFT calculation is presented. The strong vibrational bands at 354 cm(-1), 588 cm(-1) and 3022 cm(-1) are proposed for verifying the existence of the ring like, hydrogen bonded structure. Special attention was devoted to the high frequency region, where hydrogen bond vibrations are coupled to stretchings of amino and silanol groups. PMID:24021947

Volovšek, V; Danani?, V; Bistri?i?, L; Movre Šapi?, I; Furi?, K

2014-01-01

184

Zinc Nucleation and Growth in Microgravity  

NASA Technical Reports Server (NTRS)

We report our experiences with zinc nucleation in a microgravity environment aboard NASA's Reduced Gravity Research Facility. Zinc vapor is produced by a heater in a vacuum chamber containing argon gas. Nucleation is induced by cooling and its onset is easily detected visually by the appearance of a cloud of solid, at least partially crystalline zinc particles. Size distribution of these particles is monitored in situ by photon correlation spectroscopy. Samples of particles are also extracted for later analysis by SEM. The initially rapid increase in particle size is followed by a slower period of growth. We apply Scaled Nucleation Theory to our data and find that the derived critical temperature of zinc, the critical cluster size at nucleation, and the surface tension values are all in reasonably good agreement with their accepted literature values.

Michael, B. Patrick; Nuth, J. A., III; Lilleleht, L. U.; Vondrak, Richard R. (Technical Monitor)

2000-01-01

185

Comparing molecular photofragmentation dynamics in the gas and liquid phases.  

PubMed

This article explores the extent to which insights gleaned from detailed studies of molecular photodissociations in the gas phase (i.e. under isolated molecule conditions) can inform our understanding of the corresponding photofragmentation processes in solution. Systems selected for comparison include a thiophenol (p-methylthiophenol), a thioanisole (p-methylthioanisole) and phenol, in vacuum and in cyclohexane solution. UV excitation in the gas phase results in RX-Y (X = O, S; Y = H, CH3) bond fission in all cases, but over timescales that vary by ~4 orders of magnitude - all of which behaviours can be rationalised on the basis of the relevant bound and dissociative excited state potential energy surfaces (PESs) accessed by UV photoexcitation, and of the conical intersections that facilitate radiationless transfer between these PESs. Time-resolved UV pump-broadband UV/visible probe and/or UV pump-broadband IR probe studies of the corresponding systems in cyclohexane solution reveal additional processes that are unique to the condensed phase. Thus, for example, the data clearly reveal evidence of (i) vibrational relaxation of the photoexcited molecules prior to their dissociation and of the radical fragments formed upon X-Y bond fission, and (ii) geminate recombination of the RX and Y products (leading to reformation of the ground state parent and/or isomeric adducts). Nonetheless, the data also show that, in each case, the characteristics (and the timescale) of the initial bond fission process that occurs under isolated molecule conditions are barely changed by the presence of a weakly interacting solvent like cyclohexane. These condensed phase studies are then extended to an ether analogue of phenol (allyl phenyl ether), wherein UV photo-induced RO-allyl bond fission constitutes the first step of a photo-Claisen rearrangement. PMID:23552482

Harris, Stephanie J; Murdock, Daniel; Zhang, Yuyuan; Oliver, Thomas A A; Grubb, Michael P; Orr-Ewing, Andrew J; Greetham, Gregory M; Clark, Ian P; Towrie, Michael; Bradforth, Stephen E; Ashfold, Michael N R

2013-05-14

186

Gas-phase Dissociation of homo-DNA Oligonucleotides  

NASA Astrophysics Data System (ADS)

Synthetic modified oligonucleotides are of interest for diagnostic and therapeutic applications, as their biological stability, pairing selectivity, and binding strength can be considerably increased by the incorporation of unnatural structural elements. Homo-DNA is an oligonucleotide homologue based on dideoxy-hexopyranosyl sugar moieties, which follows the Watson-Crick A-T and G-C base pairing system, but does not hybridize with complementary natural DNA and RNA. Homo-DNA has found application as a bioorthogonal element in templated chemistry applications. The gas-phase dissociation of homo-DNA has been investigated by ESI-MS/MS and MALDI-MS/MS, and mechanistic aspects of its gas-phase dissociation are discussed. Experiments revealed a charge state dependent preference for the loss of nucleobases, which are released either as neutrals or as anions. In contrast to DNA, nucleobase loss from homo-DNA was found to be decoupled from backbone cleavage, thus resulting in stable products. This renders an additional stage of ion activation necessary in order to generate sequence-defining fragment ions. Upon MS3 of the primary base-loss ion, homo-DNA was found to exhibit unspecific backbone dissociation resulting in a balanced distribution of all fragment ion series.

Stucki, Silvan R.; Désiron, Camille; Nyakas, Adrien; Marti, Simon; Leumann, Christian J.; Schürch, Stefan

2013-12-01

187

Naphthol coupling monitored by infrared spectroscopy in the gas phase.  

PubMed

The reaction mechanism of copper(II)-mediated naphthol coupling in the presence of TMEDA (N,N,N',N'-tetramethylethylenediamine) is studied using infrared multiphoton dissociation (IRMPD) spectroscopy and DFT calculations. It is shown that the coupling reaction proceeds in ad hoc formed binuclear clusters [(1-H)(2)Cu(2)Cl(TMEDA)(2)](+), where (1-H) is a deprotonated naphthol molecule (methyl ester of 3-hydroxy-2-naphthoic acid). The IRMPD spectra of the isolated cluster in the gas phase reveal that it contains two uncoupled naphtholate subunits and only the irradiation promotes the coupling reaction, which is thus observed as a genuine gas-phase reaction. The driving force for the C-C coupling is a keto-enol tautomerization of the initial coupling product, and the formation of the corresponding binol in the cluster is exothermic by 0.61 eV. In contrast, analogous C-O and O-O couplings are endothermic reactions. PMID:19954233

Roithová, Jana; Milko, Petr

2010-01-13

188

Nahoon: Time-dependent gas-phase chemical model  

NASA Astrophysics Data System (ADS)

Nahoon is a gas-phase chemical model that computes the chemical evolution in a 1D temperature and density structure. It uses chemical networks downloaded from the KInetic Database for Astrochemistry (KIDA) but the model can be adapted to any network. The program is written in Fortran 90 and uses the DLSODES (double precision) solver from the ODEPACK package to solve the coupled stiff differential equations. The solver computes the chemical evolution of gas-phase species at a fixed temperature and density and can be used in one dimension (1D) if a grid of temperature, density, and visual extinction is provided. Grains, both neutral and negatively charged, and electrons are considered as chemical species and their concentrations are computed at the same time as those of the other species. Nahoon contains a test to check the temperature range of the validity of the rate coefficients and avoid extrapolations outside this range. A test is also included to check for duplication of chemical reactions, defined over complementary ranges of temperature.

Wakelam, V.

2014-09-01

189

Engine exhaust particulate and gas phase contributions to vascular toxicity.  

PubMed

Cardiovascular health effects of near-roadway pollution appear more substantial than other sources of air pollution. The underlying cause of this phenomenon may simply be concentration-related, but the possibility remains that gases and particulate matter (PM) may physically interact and further enhance systemic vascular toxicity. To test this, we utilized a common hypercholesterolemic mouse model (Apolipoprotein E-null) exposed to mixed vehicle emission (MVE; combined gasoline and diesel exhausts) for 6?h/d?×?50?d, with additional permutations of removing PM by filtration and also removing gaseous species from PM by denudation. Several vascular bioassays, including matrix metalloproteinase-9 protein, 3-nitrotyrosine and plasma-induced vasodilatory impairments, highlighted that the whole emissions, containing both particulate and gaseous components, was collectively more potent than MVE-derived PM or gas mixtures, alone. Thus, we conclude that inhalation of fresh whole emissions induce greater systemic vascular toxicity than either the particulate or gas phase alone. These findings lend credence to the hypothesis that the near-roadway environment may have a more focused public health impact due to gas-particle interactions. PMID:24730681

Campen, Matthew; Robertson, Sarah; Lund, Amie; Lucero, Joann; McDonald, Jacob

2014-05-01

190

Molecular-dynamics simulations of urea nucleation from aqueous solution.  

PubMed

Despite its ubiquitous character and relevance in many branches of science and engineering, nucleation from solution remains elusive. In this framework, molecular simulations represent a powerful tool to provide insight into nucleation at the molecular scale. In this work, we combine theory and molecular simulations to describe urea nucleation from aqueous solution. Taking advantage of well-tempered metadynamics, we compute the free-energy change associated to the phase transition. We find that such a free-energy profile is characterized by significant finite-size effects that can, however, be accounted for. The description of the nucleation process emerging from our analysis differs from classical nucleation theory. Nucleation of crystal-like clusters is in fact preceded by large concentration fluctuations, indicating a predominant two-step process, whereby embryonic crystal nuclei emerge from dense, disordered urea clusters. Furthermore, in the early stages of nucleation, two different polymorphs are seen to compete. PMID:25492932

Salvalaglio, Matteo; Perego, Claudio; Giberti, Federico; Mazzotti, Marco; Parrinello, Michele

2015-01-01

191

Surfactants from the gas phase may promote cloud droplet formation  

PubMed Central

Clouds, a key component of the climate system, form when water vapor condenses upon atmospheric particulates termed cloud condensation nuclei (CCN). Variations in CCN concentrations can profoundly impact cloud properties, with important effects on local and global climate. Organic matter constitutes a significant fraction of tropospheric aerosol mass, and can influence CCN activity by depressing surface tension, contributing solute, and influencing droplet activation kinetics by forming a barrier to water uptake. We present direct evidence that two ubiquitous atmospheric trace gases, methylglyoxal (MG) and acetaldehyde, known to be surface-active, can enhance aerosol CCN activity upon uptake. This effect is demonstrated by exposing acidified ammonium sulfate particles to 250 parts per billion (ppb) or 8 ppb gas-phase MG and/or acetaldehyde in an aerosol reaction chamber for up to 5 h. For the more atmospherically relevant experiments, i.e., the 8-ppb organic precursor concentrations, significant enhancements in CCN activity, up to 7.5% reduction in critical dry diameter for activation, are observed over a timescale of hours, without any detectable limitation in activation kinetics. This reduction in critical diameter enhances the apparent particle hygroscopicity up to 26%, which for ambient aerosol would lead to cloud droplet number concentration increases of 8–10% on average. The observed enhancements exceed what would be expected based on Köhler theory and bulk properties. Therefore, the effect may be attributed to the adsorption of MG and acetaldehyde to the gas–aerosol interface, leading to surface tension depression of the aerosol. We conclude that gas-phase surfactants may enhance CCN activity in the atmosphere. PMID:23382211

Sareen, Neha; Schwier, Allison N.; Lathem, Terry L.; Nenes, Athanasios; McNeill, V. Faye

2013-01-01

192

Development and application of a new air pollution modeling system-part I: Gas-phase simulations  

NASA Astrophysics Data System (ADS)

A new air pollution modeling system is discussed and applied. The system consists of GATOR, a gas, aerosol, transport, and radiation air quality model and MMTD, a mesoscale meteorological and tracer dispersion model. The gas-phase processes treated by GATOR include photochemistry, deposition, emissions, and gas-to-particle conversion. To solve stiff chemical rate equations, a sparse-matrix, vectorized Gear-type code (SMVGEAR) was used. The aerosol processes in GATOR include coagulation, aqueous chemistry, chemical equilibrium, condensational growth, dissolutional growth, evaporation, nucleation, emissions, deposition, and sedimentation. The transport processes include horizontal advection and diffusion and vertical convection and diffusion. Finally, the radiation algorithm calculates ultraviolet, visible, and infrared optical depths, mean intensities for photodissociation rates, and radiative heat fluxes for temperature calculations. The MMTD predicts winds, diffusion, temperature, pressure, humidity, soil moisture, and rainfall. These variables are fed to GATOR and radiative heating rates from GATOR are fed back to the MMTD. With the GATOR/MMTD system, gas-phase pollution was simulated for the Southern California Air Quality Study (SCAQ) days of 26-28 August 1987. Results were compared to surface measurements for many parameters. The model predicted normalized gross errors for ozone of 17.6% and 23.4% at 2:30 p.m. on the first and second days of simulation, respectively. Also, the normalized gross error during the first 12 h of simulation was 22%. Correct emissions and initial mixing ratios appear to be necessary for obtaining good results. Initial conditions outside the basin seem to affect results by the second and third days. Time-series plots, statistics, and a sensitivity test are discussed. Aerosol simulation results will be shown in a later work.

Jacobson, Mark Z.; Lu, Rong; Turco, Richard P.; Toon, Owen B.

193

Diamond Nucleation Using Polyethene  

NASA Technical Reports Server (NTRS)

The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.

Morell, Gerardo (Inventor); Makarov, Vladimir (Inventor); Varshney, Deepak (Inventor); Weiner, Brad (Inventor)

2013-01-01

194

Diamond nucleation using polyethene  

DOEpatents

The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.

Morell, Gerardo; Makarov, Vladimir; Varshney, Deepak; Weiner, Brad

2013-07-23

195

Why the Langevin-Debye theory of molecular polarisation fails in gas phase  

Microsoft Academic Search

The classical polarization formula of Langevin, which holds in the solid\\/liquid state, does not satisfy many experimental facts in gas phase, especially in diluted gas mixtures. The new formulation of the molecular polarization in gas phase is obtained on phenomenological grounds analysing the motion that polar molecules undergo under an electric field. It is shown that the polarization amplitude in

M. Michelini

196

Deposition nucleation viewed as homogeneous or immersion freezing in pores and cavities  

NASA Astrophysics Data System (ADS)

Heterogeneous ice nucleation is an important mechanism for the glaciation of mixed phase clouds and may also be relevant for cloud formation and dehydration at the cirrus cloud level. It is thought to proceed through different mechanisms, namely contact, condensation, immersion and deposition nucleation. Conceptually, deposition nucleation is the only pathway that does not involve liquid water, but occurs by direct water vapor deposition onto a surface. This study challenges this classical view by putting forward the hypothesis that what is called deposition nucleation is in fact pore condensation and freezing (PCF) occurring in voids and cavities that may form between aggregated primary particles and host water at relative humidity RHw < 100% because of the inverse Kelvin effect. Homogeneous ice nucleation is expected to occur below 235 K when at least one pore is filled with water. Ice nucleation in pores may also happen in immersion mode but with a lower probability because it requires at least one active site in a water filled pore. Therefore a significant enhancement in ice nucleation efficiency is expected when temperature falls below 235 K. For a deposition nucleation process from water vapor no discontinuous change in ice nucleation efficiency should occur at T = 235 K because no liquid water is involved in this process. Studies on freezing in confinement carried out on mesoporous silica materials such as SBA-15, SBA-16, MCM-41, zeolites and KIT have shown that homogeneous ice nucleation occurs abruptly at T = 230-235 K in pores with diameters (D) of 3.5-4 nm or larger but only gradually at T = 210-230 K in pores with D = 2.5-3.5 nm. Pore analysis of clay minerals shows that kaolinites exhibit pore structures with pore diameters (Dp) of 20-50 nm. The mesoporosity of illites and montmorillonites is characterized by pores with Dp = 2-5 nm. The number and size of pores is distinctly increased in acid treated montmorillonites like K10. Water adsorption isotherms of MCM-41 show that pores with Dp = 3.5-4 nm fill with water at RHw = 56-60% in accordance with an inverse Kelvin effect. Water in such pores should freeze homogeneously for T < 235 K even before relative humidity with respect to ice (RHi) reaches ice saturation. Ice crystal growth by water vapor deposition from the gas phase is therefore expected to set in as soon as RHi > 100%. Pores with D > 7.5 nm fill with water at RHi > 100% for T < 235 K and are likely to freeze homogeneously as soon as they are filled with water. Given the pore structure of clay minerals, PCF should be highly efficient for T < 235 K and may occur at T > 235 K in particles that exhibit active sites for immersion freezing within pores. Most ice nucleation studies on clay minerals and mineral dusts indeed show a strong increase in ice nucleation efficiency when temperature is decreased below 235 K in accordance with PCF and are not explicable by the classical view of deposition nucleation. PCF is probably also the prevailing ice nucleation mechanism below water saturation for glassy, soot, and volcanic ash aerosols. No case could be identified that gives clear evidence of ice nucleation by water vapor deposition onto a solid surface.

Marcolli, C.

2014-02-01

197

Musculoskeletal-induced Nucleation in Altitude Decompression Sickness  

NASA Technical Reports Server (NTRS)

Musculoskeletal activity has the potential to both improve and compromise decompression safety. Exercise enhances inert gas elimination during oxygen breathing prior to decompression (prebreathe), but it may also promote bubble nuclei formation (nucleation), which can lead to gas phase separation and bubble growth and increase the risk of decompression sickness (DCS). The timing, pattern and intensity of musculoskeletal activity and the level of tissue supersaturation may be critical to the net effect. There are limited data available to evaluate cost-benefit relationships. Understanding the relationship is important to improve our understanding of the underlying mechanisms of nucleation in exercise prebreathe protocols and to quantify risk in gravity and microgravity environments. Data gathered during NASA's Prebreathe Reduction Program (PRP) studies combined oxygen prebreathe and exercise followed by low pressure (4.3 psi; altitude equivalent of 30,300 ft [9,235 m]) microgravity simulation to produce two protocols used by astronauts preparing for extravehicular activity. Both the Phase II/CEVIS (cycle ergometer vibration isolation system) and ISLE (in-suit light exercise) trials eliminated ambulation to more closely simulate the microgravity environment. The CEVIS results (35 male, 10 female) serve as control data for this NASA/Duke study to investigate the influence of ambulation exercise on bubble formation and the subsequent risk of DCS.

Pollock, N. W.; Natoli, M. J.; Conkin, J.; Wessel, J. H., III; Gernhardt, M. L.

2014-01-01

198

Phase separation in a polarized Fermi gas with spin-orbit coupling  

SciTech Connect

We study the phase separation of a spin-polarized Fermi gas with spin-orbit coupling near a wide Feshbach resonance. As a result of the competition between spin-orbit coupling and population imbalance, the phase diagram for a uniform gas develops a rich structure of phase separation involving topologically nontrivial gapless superfluid states. We then demonstrate the phase separation induced by an external trapping potential and discuss the optimal parameter region for the experimental observation of the gapless superfluid phases.

Yi, W.; Guo, G.-C. [Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei, Anhui, 230026 (China)

2011-09-15

199

Experiments on Nucleation in Different Flow Regimes  

NASA Technical Reports Server (NTRS)

The vast majority of metallic engineering materials are solidified from the liquid phase. Understanding the solidification process is essential to control microstructure, which in turn, determines the properties of materials. The genesis of solidification is nucleation, where the first stable solid forms from the liquid phase. Nucleation kinetics determine the degree of undercooling and phase selection. As such, it is important to understand nucleation phenomena in order to control solidification or glass formation in metals and alloys. Early experiments in nucleation kinetics were accomplished by droplet dispersion methods. Dilitometry was used by Turnbull and others, and more recently differential thermal analysis and differential scanning calorimetry have been used for kinetic studies. These techniques have enjoyed success; however, there are difficulties with these experiments. Since materials are dispersed in a medium, the character of the emulsion/metal interface affects the nucleation behavior. Statistics are derived from the large number of particles observed in a single experiment, but dispersions have a finite size distribution which adds to the uncertainty of the kinetic determinations. Even though temperature can be controlled quite well before the onset of nucleation, the release of the latent heat of fusion during nucleation of particles complicates the assumption of isothermality during these experiments. Containerless processing has enabled another approach to the study of nucleation kinetics. With levitation techniques it is possible to undercool one sample to nucleation repeatedly in a controlled manner, such that the statistics of the nucleation process can be derived from multiple experiments on a single sample. The authors have fully developed the analysis of nucleation experiments on single samples following the suggestions of Skripov. The advantage of these experiments is that the samples are directly observable. The nucleation temperature can be measured by noncontact optical pyrometry, the mass of the sample is known, and post-processing analysis can be conducted on the sample. The disadvantages are that temperature measurement must have exceptionally high precision, and it is not possible to isolate specific heterogeneous sites as in droplet dispersions. Levitation processing of refractory materials in ultra high vacuum provides an avenue to conduct these kinetic studies on single samples. Two experimental methods have been identified where ultra high vacuum experiments are possible; electrostatic levitation in ground-based experiments and electromagnetic processing in low earth orbit on TEMPUS. Such experiments, reported here, were conducted on zirconium. Liquid zirconium is an excellent solvent and has a high solubility for contaminants contained in the bulk material as well as those contaminants found in the vacuum environment. Oxides, nitrides, and carbides do not exist in the melt, and do not form on the surface of molten zirconium, for the materials and vacuum levels used in this study. Ground-based experiments with electrostatic levitation have shown that the statistical nucleation kinetic experiments are viable and yield results which are consistent with classical nucleation theory. The advantage of low earth orbit experiments is the ability to vary the flow conditions in the liquid prior to nucleation. The put-pose of nucleation experiments in TEMPUS was to examine.

Bayuzick, R. J.; Hofmeister, W. H.; Morton, C. M.; Robinson, M. B.

1998-01-01

200

Synthesis and Gas Phase Thermochemistry of Germanium-Containing Compounds  

SciTech Connect

The driving force behind much of the work in this dissertation was to gain further understanding of the unique olefin to carbene isomerization observed in the thermolysis of 1,1-dimethyl-2-methylenesilacyclobutane by finding new examples of it in other silicon and germanium compounds. This lead to the examination of a novel phenylmethylenesilacyclobut-2-ene, which did not undergo olefin to carbene rearrangement. A synthetic route to methylenegermacyclobutanes was developed, but the methylenegermacyclobutane system exhibited kinetic instability, making the study of the system difficult. In any case the germanium system decomposed through a complex mechanism which may not include olefin to carbene isomerization. However, this work lead to the study of the gas phase thermochemistry of a series of dialkylgermylene precursors in order to better understand the mechanism of the thermal decomposition of dialkylgermylenes. The resulting dialkylgermylenes were found to undergo a reversible intramolecular {beta} C-H insertion mechanism.

Nathan Robert Classen

2002-12-31

201

Gas-phase synthesis of magnetic metal/polymer nanocomposites.  

PubMed

Highly magnetic metal Co nanoparticles were produced via reducing flame spray pyrolysis, and directly coated with an epoxy polymer in flight. The polymer content in the samples varied between 14 and 56 wt% of nominal content. A homogenous dispersion of Co nanoparticles in the resulting nanocomposites was visualized by electron microscopy. The size and crystallinity of the metallic fillers was not affected by the polymer, as shown by XRD and magnetic hysteresis measurements. The good control of the polymer content in the product nanocomposite was shown by elemental analysis. Further, the successful polymerization in the gas phase was demonstrated by electron microscopy and size measurements. The presented effective, dry and scalable one-step synthesis method for highly magnetic metal nanoparticle/polymer composites presented here may drastically decrease production costs and increase industrial yields. PMID:25422410

Starsich, Fabian H L; Hirt, Ann M; Stark, Wendelin J; Grass, Robert N

2014-12-19

202

Conformational Study of Taurine in the Gas Phase  

NASA Astrophysics Data System (ADS)

The conformational preferences of the amino sulfonic acid taurine (NH2-CH2-CH2-SO3H) have been investigated in the gas phase by laser ablation molecular beam Fourier transform microwave spectroscopy (LA-MB-FTMW) in the 6-14 GHz frequency range. One conformer has been observed, and its rotational, centrifugal distortion, and hyperfine quadrupole coupling constants have been determined from the analysis of its rotational spectrum. Comparison of the experimental constants with those calculated theoretically identifies the detected conformer unambiguously. The observed conformer of taurine is stabilized by an intramolecular hydrogen bond O-H···N between the hydrogen of the sulfonic acid group and the nitrogen atom of the amino group.

Cortijo, Vanessa; Sanz, M. Eugenia; López, Juan C.; Alonso, José L.

2009-08-01

203

Optically based diagnostics for gas-phase laser development  

NASA Astrophysics Data System (ADS)

In this paper we describe several diagnostics that we have developed to assist the development of high power gas phase lasers including COIL, EOIL, and DPAL. For COIL we discuss systems that provide sensitive measurements of O2(a), small signal gain, iodine dissociation, and temperature. These are key operational parameters within COIL, and these diagnostics have been used world-wide to gain a better understanding of this laser system. Recently, we have developed and integrated a similar suite of diagnostics for scaling the EOIL system and will provide examples of current studies. We are also developing diagnostics for the emerging DPAL laser. These include monitors for small signal gain that will provide both a more fundamental understanding of the kinetics of DPAL and valuable data for advanced resonator design. We will stress the application of these diagnostics to realistic laser systems.

Rawlins, Wilson T.; Lee, Seonkyung; Galbally-Kinney, Kristin L.; Kessler, William J.; Hicks, Adam J.; Konen, Ian M.; Plumb, Emily P.; Davis, Steven J.

2010-11-01

204

Optical properties of anthocyanins in the gas phase  

NASA Astrophysics Data System (ADS)

The gas-phase optical properties of the six most common anthocyanins are studied using time-dependent density-functional theory. Different anthocyanins are classified into three groups, according to the number of low-frequency peaks displayed in the UV-vis spectrum. This behavior is analyzed in terms of one-electron transitions and interaction effects, the latter being rationalized using a suitable double-pole model. Moving from PBE to hybrid exchange-correlation functionals results in a hypsochromic shift of the optical gap. While the colors thus predicted do not quite match those observed in solution, thus highlighting the importance of solvation effects, adoption of hybrid functionals remarkably determines a greater chromatic uniformity of different molecules, in qualitative agreement with experimental evidence in acidic solutions.

Ge, Xiaochuan; Calzolari, Arrigo; Baroni, Stefano

2015-01-01

205

Infrared photodissociation spectroscopy of protonated neurotransmitters in the gas phase  

NASA Astrophysics Data System (ADS)

Protonated neurotransmitters have been produced in the gas phase via a novel photochemical scheme: complexes of the species of interest, 1-phenylethylamine, 2-amino-1-phenylethanol and the diastereo-isomers, ephedrine and pseudoephedrine, with a suitable proton donor, phenol (or indole), are produced in a supersonic expansion and ionized by resonant two photon ionization of the donor. Efficient proton transfer generates the protonated neurotransmitters, complexed to a phenoxy radical. Absorption of infrared radiation, and subsequent evaporation of the phenoxy tag, coupled with time of flight mass spectrometry, provides vibrational spectra of the protonated (and also hydrated) complexes for comparison with the results of quantum chemical computation. Comparison with the conformational structures of the neutral neurotransmitters (established previously) reveals the effect of protonation on their structure. The photochemical proton transfer strategy allows spectra to be recorded from individual laser shots and their quality compares favourably with that obtained using electro-spray or matrix assisted laser desorption ion sources.

MacLeod, N. A.; Simons, J. P.

2007-03-01

206

Uncertainties in gas-phase atmospheric iodine chemistry  

NASA Astrophysics Data System (ADS)

We present a comprehensive chemical mechanism for gas-phase iodine, to be used for modelling tropospheric chemistry. The mechanism has been compiled from evaluated data and individual literature studies, where available; a number of key processes have not been studied experimentally or theoretically and in these cases estimations have been made. The uncertainty associated with these assumptions is evaluated. We analyze the mechanism using a box-model under a variety of boundary layer scenarios - representative of environments where iodine species have been observed - to study the response of the chemical system to changes in the kinetic parameters of selected reactions. We focus in particular on key species such as IO, OIO, INO3 and I2Oy and the impact of iodine chemistry on ozone formation and HOx levels. The results indicate that the chemical system is most sensitive to reactions leading to comparatively stable iodine compounds, which should be a focus of future laboratory studies.

Sommariva, R.; Bloss, W. J.; von Glasow, R.

2012-09-01

207

Silicon Nanowire-Based Devices for Gas-Phase Sensing  

PubMed Central

Since their introduction in 2001, SiNW-based sensor devices have attracted considerable interest as a general platform for ultra-sensitive, electrical detection of biological and chemical species. Most studies focus on detecting, sensing and monitoring analytes in aqueous solution, but the number of studies on sensing gases and vapors using SiNW-based devices is increasing. This review gives an overview of selected research papers related to the application of electrical SiNW-based devices in the gas phase that have been reported over the past 10 years. Special attention is given to surface modification strategies and the sensing principles involved. In addition, future steps and technological challenges in this field are addressed. PMID:24368699

Cao, Anping; Sudhölter, Ernst J.R.; de Smet, Louis C.P.M.

2014-01-01

208

Tautomerism of cytosine probed by gas phase IR spectroscopy  

NASA Astrophysics Data System (ADS)

The tautomerism of the gaseous protonated cytosine is studied using infrared multiple photon dissociation (IRMPD) spectroscopy of singly hydrated complexes of protonated cytosine in the 2700-3750 cm-1 wavenumber range. The hydrated complexes are formed through argon-mediated collisions between bare electrosprayed cytosine and low-pressure water vapor. In the spectra, where X-H (XC, O, and N) stretching vibrations are probed, evidence is found for the coexistence in the gas phase of hydrated complexes of two different cytosine tautomers. As the addition of a water molecule to either tautomer of protonated cytosine is energetically highly unlikely to induce interconversion, it is deduced that both C(2)O and N(3) protonated tautomers of cytosine are formed under electrospray conditions.

Bakker, Joost M.; Salpin, Jean-Yves; Maître, Philippe

2009-06-01

209

Structures of platinum oxide clusters in the gas phase.  

PubMed

The structures of small gas-phase Pt(n)O(2m)(+) (n = 1-6, m = 1, 2) cluster cations have been investigated in a combined infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory (DFT) study. On the basis of the infrared spectra obtained, it is concluded that in most clusters oxygen is bound dissociatively, preferring 2-fold bridge binding motifs, sometimes combined with singly coordinated terminal binding. Comparison of the oxide cluster structures with those of bare cationic platinum clusters reported previously reveals major structural changes induced in the platinum core upon oxygen binding. For some cluster sizes the presence of the Ar messenger atom(s) is found to induce a significant change in the observed cluster structure. PMID:22894744

Kerpal, Christian; Harding, Dan J; Hermes, Alexander C; Meijer, Gerard; Mackenzie, Stuart R; Fielicke, André

2013-02-14

210

Gas phase structures of peroxides: experiments and computational problems.  

PubMed

Gas-phase structures of several organic and inorganic peroxides X-O-O-X and X-O-O-X', which have been determined experimentally by gas electron diffraction and/or microwave spectroscopy, are discussed. The O?O bond length in these peroxides varies from 1.481(8) Å in Me3 SiOOSiMe3 to 1.214(2) Å in FOOF and the dihedral angle ?(XO-OX) between 0° in HC(O)O-OH and near 180° in Bu(t) O-OBu(t) . Some of the peroxides cause problems for quantum chemistry, since several computational methods fail to reproduce the experimental structures. Extreme examples are MeO-OMe and FO-OF. In the case of MeO-OMe only about half of the more than 100 computational methods reported in the literature reproduce the experimentally determined double-minimum shape of the torsional potential around the O?O bond correctly. For FO-OF only a small number of close to 200 computational methods reproduce the O?O and O?F bond lengths better than ±0.02 Å. PMID:25475056

Oberhammer, Heinz

2015-02-01

211

Gas phase hydrogen permeation in alpha titanium and carbon steels  

NASA Technical Reports Server (NTRS)

Commercially pure titanium and heats of Armco ingot iron and steels containing from 0.008-1.23 w/oC were annealed or normalized and machined into hollow cylinders. Coefficients of diffusion for alpha-Ti and alpha-Fe were determined by the lag-time technique. Steady state permeation experiments yield first power pressure dependence for alpha-Ti and Sievert's law square root dependence for Armco iron and carbon steels. As in the case of diffusion, permeation data confirm that alpha-titanium is subject to at least partial phase boundary reaction control while the steels are purely diffusion controlled. The permeation rate in steels also decreases as the carbon content increases. As a consequence of Sievert's law, the computed hydrogen solubility decreases as the carbon content increases. This decreases in explained in terms of hydrogen trapping at carbide interfaces. Oxidizing and nitriding the surfaces of alpha-titanium membranes result in a decrease in the permeation rate for such treatment on the gas inlet surfaces but resulted in a slight increase in the rate for such treatment on the gas outlet surfaces. This is explained in terms of a discontinuous TiH2 layer.

Johnson, D. L.; Shah, K. K.; Reeves, B. H.; Gadgeel, V. L.

1980-01-01

212

Gas phase photolysis of pinonaldehyde in the presence of sunlight  

NASA Astrophysics Data System (ADS)

The photolysis of pinonaldehyde in the presence of sunlight and in the presence/absence of an OH radical scavenger (cyclohexane) was studied in a large outdoor smog chamber. More than nine reaction products were identified or tentatively identified and quantified in this study using gas chromatography-mass spectrometry. Carbon yields for pinonaldehyde photolysis in the absence of an OH scavenger are: norpinonaldehyde (21.7%); pinonic acid (11.2%); 3-acetyl-2,2-dimethyl-cyclobutyl-methanol (5.3%); 2,2,3-trimethyl-cyclobutylethanone (2.9%); and 10-oxonorpinonaldehyde (1.9%). Carbon yields for pinonaldehyde photolysis in the presence of cyclohexane are: norpinonaldehyde (20.1%); pinonic acid (0.4%); 3-acetyl-2,2-dimethyl-cyclobutyl-methanol (2.7%); 2,2,3-trimethyl-cyclobutyl-ethanone (1.3%); and 10-oxonorpinonaldehyde (1.0%). The uncertainty in the yield data is estimated to be ˜26%. The results show that pinonaldehyde photolysis is an important part of its overall atmospheric chemistry. A detailed mechanism for pinonaldehyde photolysis in the presence/absence of cyclohexane is proposed, and a kinetic mechanism was used to simulate the gas phase reactions of pinonaldehyde. Observed temporal profiles of pinonaldehyde and its photooxidation products were used to estimate photolysis quantum yields for pinonaldehyde. The atmospheric implications of the data are discussed.

Jaoui, M.; Kamens, R. M.

213

Estimation of gas phase mixing in packed beds  

SciTech Connect

An improved model is presented for estimation of the mixing of gaseous species in a packed bed for fuel conversion. In particular, this work clarifies the main characteristics of mixing of volatiles and oxidizers in a burning bed of high-volatile solid fuel. Expressions are introduced to represent the active role of degradation of the solid particles in the mixing within the gas phase. During drying and devolatilization the solids modify the behavior of the gas flow: the volatiles released from the surface of the particles increase the turbulence in the system, and hence the rates of the homogeneous reactions under mixing-limited conditions. Numerical experiments are carried out to test the validity of this conclusion regarding mixing in different geometries. The flow of volatiles leaving the fuel particles is shown to contribute significantly to mixing, especially at low air flows through a bed. However, the fraction of the particle surface where volatiles are released and its orientation in the bed should be better determined in order to increase the accuracy of the estimates of turbulent mixing. (author)

Frigerio, S. [CMIC Dipartimento di Chimica, Materiali e Ingegneria Chimica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milan (Italy); Thunman, H.; Leckner, B.; Hermansson, S. [Department of Energy Conversion, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)

2008-04-15

214

Star Formation and Gas Phase History of the Cosmic Web  

E-print Network

We present a new method of tracking and characterizing the environment in which galaxies and their associated circumgalactic medium evolve. We use a structure finding algorithm we developed to self-consistently parse and follow the evolution of poor clusters, filaments and voids in large scale simulations. We trace the complete evolution of the baryons in the gas phase and the star formation history within each structure in our simulated volume. We vary the structure measure threshold to probe the complex inner structure of star forming regions in poor clusters, filaments and voids. We find the majority of star formation occurs in cold, condensed gas in filaments at intermediate redshifts (z ~ 3). We also show that much of the star formation above a redshift z = 3 occurs in low contrast regions of filaments, but as the density contrast increases at lower redshift star formation switches to the high contrast regions, or inner parts, of filaments. Since filaments bridge the void and cluster regions, it suggests...

Snedden, Ali; Phillips, Lara Arielle; Mathews, Grant; Suh, In-Saeng

2014-01-01

215

AEROSOL NUCLEATION AND GROWTH DURING LAMINAR TUBE FLOW: MAXIMUM SATURATIONS AND NUCLEATION RATES. (R827354C008)  

EPA Science Inventory

An approximate method of estimating the maximum saturation, the nucleation rate, and the total number nucleated per second during the laminar flow of a hot vapour–gas mixture along a tube with cold walls is described. The basis of the approach is that the temperature an...

216

Ice nucleation terminology  

NASA Astrophysics Data System (ADS)

Progress in the understanding of ice nucleation is being hampered by the lack of uniformity in how some terms are used in the literature. This even extends to some ambiguity of meanings attached to some terms. Suggestions are put forward here for common use of terms. Some are already well established and clear of ambiguities. Others are less engrained and will need a conscious effort in adoption. Evolution in the range of systems where ice nucleation is being studied enhances the need for a clear nomenclature. The ultimate limit in the clarity of definitions is, of course, the limited degree to which ice nucleation processes are understood.

Vali, G.; DeMott, P.; Möhler, O.; Whale, T. F.

2014-08-01

217

Independent component analysis of the interface fluctuations of gas\\/liquid two-phase flow  

Microsoft Academic Search

It is important to study the interface fluctuations between the two phases in a gas\\/liquid flow to achieve an in-depth understanding of the mixture flow and subsequent optimization of industrial processes. This paper presents a study of the interface fluctuations between the gas and liquid phases in a pipeline. Experimental data are obtained from a gas\\/liquid two-phase flow rig through

Yanbin Xu; Huaxiang Wang; Ziqiang Cui; Feng Dong; Yong Yan

2009-01-01

218

Interfacial process of nucleation and molecular nucleation templator  

NASA Astrophysics Data System (ADS)

Interfacial effects of nucleation inhibition and promotion were identified from the nucleation of paracetamol. Unlike the classic interfacial effects, which are caused by the change in nucleation barrier, the nonepitaxial interfacial effects are only associated with kink integration kinetics. Methylparaben inhibits nucleation by increasing the desolvation free energy barrier, which is revealed as the nonepitaxial interfacial effect of nucleation inhibition. Polysaccharide revealed its nonepitaxial interfacial effects of nucleation promotion by lowering the conformation entropic barrier via liquid molecule preordering. Polysaccharide can be regarded as an example of molecular nucleation promoter based on the nonepitaxial interfacial effects.

Liu, X. Y.

2001-07-01

219

Full field gas phase velocity measurements in microgravity  

NASA Technical Reports Server (NTRS)

Measurement of full-field velocities via Particle Imaging Velocimetry (PIV) is common in research efforts involving fluid motion. While such measurements have been successfully performed in the liquid phase in a microgravity environment, gas-phase measurements have been beset by difficulties with seeding and laser strength. A synthesis of techniques developed at NASA LeRC exhibits promise in overcoming these difficulties. Typical implementation of PIV involves forming the light from a pulsed laser into a sheet that is some fraction of a millimeter thick and 50 or more millimeters wide. When a particle enters this sheet during a pulse, light scattered from the particle is recorded by a detector, which may be a film plane or a CCD array. Assuming that the particle remains within the boundaries of the sheet for the second pulse and can be distinguished from neighboring particles, comparison of the two images produces an average velocity vector for the time between the pulses. If the concentration of particles in the sampling volume is sufficiently large but the particles remain discrete, a full field map may be generated.

Griffin, Devon W.; Yanis, William

1995-01-01

220

The influence of dopants and impurities on the nucleation and growth of diamond by chemical vapor deposition  

NASA Astrophysics Data System (ADS)

This work describes the influence of non carbon elements, oxygen, boron, and silicon, in diamond CVD, including the nucleation of diamond particles in the gas phase and growth of diamond films by a cyclic process. Gas phase nucleation of diamond was achieved by microwave plasma decomposition of methane and a dopant gas, sometimes with the addition of hydrogen. The dopant elements, boron or silicon, were intended to form solid carbide seeds which could serve as heterogeneous surfaces to promote diamond nucleation. Boron was found to be an effective aid to the gas phase nucleation of diamond. Diamond nucleation was detected at all levels of boron concentration and over wider ranges of pressure, power, and composition than in the case of homogeneous nucleation. The yield of amorphous carbon increased as well. The amorphous carbon proved to be resistant to oxidizing acids, which made purification of the diamond phase more difficult. Silicon doping of the reactant gases produced no diamond but did make large quantities of a weakly bonded amorphous hydrogenated silicon carbide, a-Si:C:H. The difference between the effect of boron and silicon on diamond nucleation is attributed to their influences on the growth kinetics of the diamond nuclei, rather than their tendency to form stable carbide seeds. Diamond films were grown by a cyclic CVD process, in which the reactant gas is rapidly alternated between a hydrocarbon growth mixture and an oxygenated etchant. The interaction of carbon, oxygen, and silicon in the cyclic process was investigated after a poisoning effect was discovered, characterized by a strong time dependent decline in the growth rate and quality. Chemical analysis, experimental variants, and thermodynamic analysis identified silicon from the substrate as the poisoning agent. The role of oxygen in the cyclic process was investigated by a combination of three cycle experiments, oxygen concentration studies, and homoepitaxial growth. Oxygenated species were found to be the primary etchants in the cyclic process, however their effectiveness is greatly reduced by hydrogenation prior to oxygen exposure. Oxygen influences the development of film morphology, causing extensive ledge formation and high relief structures on <001>.

Howard, William Neville

221

ELECTRONIC STRUCTURE AND SPECTROSCOPY IN THE GAS AND CONDENSED PHASE: METHODOLOGY AND APPLICATIONS.  

E-print Network

ELECTRONIC STRUCTURE AND SPECTROSCOPY IN THE GAS AND CONDENSED PHASE: METHODOLOGY AND APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 iii #12;3 Future work 96 3.1 Methodology

Krylov, Anna I.

222

Comparison of photoluminescence of carbon nanotube/ZnO nanostructures synthesized by gas- and solution-phase transport  

NASA Astrophysics Data System (ADS)

Multiwalled carbon nanotubes (MWCNTs)/ZnO heterostructures were synthesized by two different processes: (1) gas-phase transport (GPT) and nucleation of Zn powders and (2) solution-phase transport (SPT) chemical reaction of zinc nitrate solution on the MWCNTs. Transmission electron microscopy and X-ray diffraction analysis indicated that the ZnO nanostructures on the MWCNTs from the GPT and SPT processes were poly- and single-crystal hexagonal wurtzite structure, respectively. The major photoluminescence (PL) spectra of our MWCNT/ZnO hybrid, excited at 380 nm and 550 nm, were presented. The PL intensity of the MWCNT/ZnO coaxial nanostructures behaves differently depending on the ZnO synthesis methods on the MWCNTs. The MWCNT/ZnO heterostructures synthesized using the GPT process were more efficient than those synthesized by SPT process in enhancing the PL intensity around the near-band-edge emission region. However, the emission enhancement around defect region was mostly attributed to increase in the O vacancy concentration in the ZnO on the MWCNTs during the SPT process.

Jin, Changhyun; Lee, Seawook; Kim, Chang-Wan; Park, Suyoung; Lee, Chongmu; Lee, Dongjin

2015-02-01

223

Energetics of Selected Gas Phase Ion-Molecule Reactions  

NASA Astrophysics Data System (ADS)

The energetics of the gas phase negative ion-molecule association reactions M + X^{-} = McdotX^ {-}, where M are substituted benzenes, quinones and ethylenes and X^{-} are the halide ions (F^{-} , Cl^{-}, Br ^{-} and I^{ -}), were determined by equilibrium measurements with the pulsed electron high pressure mass spectrometer (PHPMS). Evaluation of the equilibrium constants for the halide association (XA) reactions leads directly to absolute bond free energy determinations, -DeltaG _sp{XA}{circ}, in McdotX^{- }. Under conditions where halide association equilibria could not be measured directly, relative bond free energies, -DeltaDeltaG _sp{XA}{circ}, were obtained by measurements of the transfer equilibria McdotX^{-} + M^' = M + cdotM^'cdot X^{-}. Combining -DeltaDeltaG_sp {XA}{circ} values with directly determined -DeltaG _sp{XA}{circ} values leads to further absolute bond free energy determinations. The hydrogen bond free energies in the singly substituted phenol complexes YPhOHcdotBr ^{-}, combined with previous data for X^{-} = Cl ^{-} and I^{ -} from this laboratory, are used to examine the substituent effects on hydrogen bonding. The dominant contribution to YPhOHcdotBr ^{-} stabilization, where the extent of proton transfer from YPhOH to Br^{ -} is small, is due to the field effects of the substituents with pi delocalization playing only a small part. Thus, the correlation with the acidity of YPhOH, where pi delocalization is important, is not very close. Substituent effect analysis of experimentally determined bond free energies and quantum mechanical calculations are used to gain structural information on the complexes McdotX^{-} where M does not possess substituents with protic hydrogens. The results indicate the complexes M cdotX^{-} have a variety of structures, depending on X^ {-} and the nature of the substituents. The temperature dependence of the equilibrium constants for the gas phase reactions HO^ - + HOH = HO^-cdotHOH and CH_3O^- + HOCH_3 = CH_3O ^-cdotHOCH_3 was measured with the PHPMS. The enthalpy and entropy changes were obtained from van't Hoff plots of the equilibrium constants. The enthalpy changes were found to be in good agreement with experimentally determined values reported by Meot-Ner and Sieck and recent theoretical results. The agreement for the entropy changes is found not to be as good. The electron affinities of 20 cyclic diones, mostly substituted maleic and phthalic anhydrides and maleimides and phthalimides, were determined with the PHPMS by measuring gas phase electron transfer equilibria A^ {-} + B = A + B^{ -} involving these compounds and reference compounds whose electron affinities were determined previously. The effects of substituents on electron affinities are similar to those observed previously for other groups of organic compounds.

Paul, Gary John Charles

1990-01-01

224

Measurement of Gas-phase Acids in Diesel Exhaust  

NASA Astrophysics Data System (ADS)

Gas-phase acids were measured using chemical ionization mass spectrometry (CIMS) as part of the Diesel Engine Emission Research Experiment (DEERE). The CIMS technique, utilizing acetate ion (CH3COO-) as a reagent ion, proved to be a rapid (measurements on the order of seconds) and sensitive (several counts/pptv) method of quantifying the acid emissions. Diluted diesel exhaust measurements were made from a Constant Volume Sampling dilution tunnel using a light duty (1.9L turbocharged Volkswagen Jetta TDI) diesel engine equipped with an OEM diesel oxidation catalyst and exhaust gas recirculation, mounted on an engine dynamometer. Acids measured included isocyanic, nitrous, nitric, propionic and sum of lactic and oxalic, as well as other unidentified compounds. Complimentary measurements of CO, CO2, Total Hydrocarbon (THC), and NOx, were also performed. Several engine modes (different engine rpm and torque outputs) at steady state were examined to determine their effect on acid emissions. Emission rates with respect to NOx and fuel based emission factors were determined. Measurements of HONO fuel emission factors agree well with real-world measurements within a traffic tunnel.1 The first estimate of isocyanic acid emission factors from a diesel engine is reported, and suggests that the emission of this highly toxic compound in diesel exhaust should not be ignored. 1. Kurtenbach, R., Becker, K. H., Gomes, J. A. G., Kleffmann, J.,Lorzer, J. C., Spittler, M., Wiesen, P., Ackermann, R., Geyer, A.,and Platt, U.: Investigations of emissions and heterogeneous formation of HONO in a road traffic tunnel, Atmos. Environ., 35, 3385-3394, doi:10.1016/S1352-2310(01)00138-8, 2001.

Wentzell, J. J.; Liggio, J.; Li, S.; Vlasenko, A. L.; Staebler, R. M.; Brook, J.; Lu, G.; Poitras, M.; Chan, T.

2012-12-01

225

Infrared spectra of dimethylphenanthrenes in the gas phase.  

PubMed

Infrared spectra of atmospherically and astronomically important dimethylphenanthrenes (DMPs), namely 1,9-DMP, 2,4-DMP, and 3,9-DMP, were recorded in the gas phase from 400 to 4000 cm(-1) with a resolution of 0.5 cm(-1) at 110 °C using a 7.2 m gas cell. DFT calculations at the B3LYP/6-311G** level were carried out to get the harmonic and anharmonic frequencies and their corresponding intensities for the assignment of the observed bands. However, spectral assignments could not be made unambiguously using anharmonic or selectively scaled harmonic frequencies. Therefore, the scaled quantum mechanical (SQM) force field analysis method was adopted to achieve more accurate assignments. In this method force fields instead of frequencies were scaled. The cartesian force field matrix obtained from the gaussian calculations was converted to a nonredundant local coordinate force field matrix and then the force fields were scaled to match experimental frequencies in a consistent manner using a modified version of the UMAT program of the QCPE package. Potential energy distributions (PEDs) of the normal modes in terms of nonredundant local coordinates obtained from these calculations helped us derive the nature of the vibration at each frequency. The intensity of observed bands in the experimental spectra was calculated using estimated vapor pressures of the DMPs. An error analysis of the mean deviation between experimental and calculated intensities reveal that the observed methyl C-H stretching intensity deviates more compared to the aromatic C-H and non C-H stretching bands. PMID:21797244

Das, Prasanta; Arunan, E; Das, Puspendu K

2012-06-21

226

DETERMINATION OF GAS-PHASE DIMETHYL SULFATE AND MONOMETHYL HYDROGEN SULFATE  

EPA Science Inventory

Analytical techniques have been developed for the collection and determination of gas phase dimethyl sulfate and monomethyl sulfuric acid in the flue lines and plumes of power plants and in the ambient atmosphere. The techniques involve the collection of the gas phase species in ...

227

Theoretical Analysis of Oscillatory Burning of Homogeneous Solid Propellant Including Non-Steady Gas Phase Effects  

Microsoft Academic Search

This paper presents a theoretical analysis of the linear burning response of an homogeneous solid propellant to pressure fluctuations. The major contribution of this work is to take into account the non-steady effects of the gas phase in a systematic way and thus, eliminate the strong limitation of previous analysis in which the gas-phase is assumed to respond in a

PAUL CLAVIN; DAVID LAZIMI

1992-01-01

228

Modeling Gas Phase RDX Combustion with Intrinsic Low Dimensional Manifolds 1 Sandeep Singh2  

E-print Network

- ated with full models of gas phase RDX combustion, and thus significantly improve computational a wide variety of thermochemical phenomena, the effects of detailed finite rate chemistry must link between traditional collision-based gas phase chemistry and fundamental fluid mechanics. However

229

OXYGEN GAS-PHASE ABUNDANCE REVISITED M. K. Andre,1,2  

E-print Network

OXYGEN GAS-PHASE ABUNDANCE REVISITED M. K. Andre´,1,2 C. M. Oliveira,2 J. C. Howk,2 R. Ferlet,1 J gas-phase oxygen abundance along the sight lines toward 19 early-type Galactic stars at an average mag�1 with a standard deviation of 15% is consistent with previous surveys. The mean oxygen abundance

Howk, Jay Christopher

230

DEMONSTRATION OF FUEL CELLS TO RECOVER ENERGY FROM LANDFILL GAS: PHASE II. PRETREATMENT SYSTEM PERFORMANCE MEASUREMENT  

EPA Science Inventory

The report describes Phase II of a demonstration of the utilization of commercial phosphoric acid fuel cells to recover energy from landfill gas. This phase consisted primarily of the construction and testing of a Gas Pretreatment Unit (GPU) whose function is to remove those impu...

231

DEMONSTRATION OF FUEL CELLS TO RECOVER ENERGY FROM LANDFILL GAS: PHASE II. PRETREATMENT SYSTEM PERFORMANCE MEASUREMENT  

EPA Science Inventory

The report describes-Phase II of a demonstration of the utilization of commercial phosphoric acid fuel cells to recover energy from landfill gas. his phase consisted primarily of the construction and testing of a Gas Pretreatment Unit (GPU) whose function is to remove those impur...

232

Volumes of Individual Amino Acid Residues in Gas-Phase Peptide Ions  

E-print Network

Volumes of Individual Amino Acid Residues in Gas-Phase Peptide Ions Anne E. Counterman and David E calculations have been combined to extract average volumes of amino acid residues in gas-phase peptide ions [XxxnLys+H]+ (where Xxx is any amino acid except Lys, Arg, His, and Cys, and n ) 4 to 8). The results

Clemmer, David E.

233

Pressure dependent phase stability transformations of GaS: A first principles study  

E-print Network

Pressure dependent phase stability transformations of GaS: A first principles study Bin Wen a principle calculations are used to determine the pressure dependent phase stability transformations for GaS polytypes at pressures up to 1000 GPa. Our results indicate that the relative stability sequence changes

Melnik, Roderick

234

Gas-phase study of Fe sup + -benzyne with alkanes  

SciTech Connect

The unimolecular chemistry of Fe{sup +}-benzyne and its reactivity with small alkanes in the gas phase are studied by Fourier transform mass spectrometry (FTMS). Collision-induced dissociation of Fe{sup +}-benzyne yields benzyne loss exclusively. In contrast, photodissociation of Fe{sup +}-benzyne yields not only cleavage of benzyne from Fe{sup +}, but competitive loss of C{sub 2}H{sub 2} and C{sub 4}H{sub 2} as well. The Fe{sup +}-benzyne is formed from chlorobenzene by loss of HCl. This dehydrochlorination of chlorobenzene also occurs in secondary reactions up to six times forming products of the type Fe{sup +}-polyphenylene. Fe{sup +}-benzyne reacts with alkanes larger than methane to form a wide variety of product ions by mechanisms including hydrogenation and methanation of the benzyne ligand. All of the product ions can be explained by mechanisms based on Fe{sup +} insertion into either C-C or C-H bonds as the reaction-initiating step, followed by either alkyl or H migration from Fe{sup +} onto the benzyne ligand or, alternatively, by the migratory insertion of benzyne into a metal-carbon or metal-hydrogen bond. Photodissociation and ion-molecule reaction studies yield a value for the metal-ligand bond energy of D{degree} (Fe{sup +}-benzyne) = 76 {plus minus} 10 kcal/mol.

Yongqing Huang; Freiser, B.S. (Purdue Univ., West Lafayette, IN (USA))

1989-03-29

235

Seven-coordinate homoleptic metal carbonyls in the gas phase.  

PubMed

Gas-phase metal carbonyl cations of the vanadium-group metals (V(+), Nb(+), Ta(+)) were produced in a molecular beam by laser vaporization and then mass-analyzed and size-selected in a time-of-flight spectrometer and studied with IR laser photodissociation spectroscopy in the carbonyl-stretching region. The abundances in the mass spectra, the fragmentation patterns, and the IR spectra provided a combined approach that revealed the coordination numbers in these systems. Although seven-coordinate structures would have 18 electrons in each case, V(CO)(6)(+) was found to be formed rather than V(CO)(7)(+). Nb(+) formed both six- and seven-coordinate species, while Ta(+) formed only the Ta(CO)(7)(+) complex. Density functional theory computations were used to predict the IR spectra for these systems, which are dramatically different for the six- and seven-coordinate structures and in excellent agreement with the measurements. V(CO)(6)(+) and Nb(CO)(6)(+) have structures slightly distorted from octahedral, while Nb(CO)(7)(+) and Ta(CO)(7)(+) have C(3v) capped octahedral structures. PMID:19522497

Ricks, Allen M; Reed, Zach D; Duncan, Michael A

2009-07-01

236

Surface plasmon sensing of gas phase contaminants using optical fiber.  

SciTech Connect

Fiber-optic gas phase surface plasmon resonance (SPR) detection of several contaminant gases of interest to state-of-health monitoring in high-consequence sealed systems has been demonstrated. These contaminant gases include H{sub 2}, H{sub 2}S, and moisture using a single-ended optical fiber mode. Data demonstrate that results can be obtained and sensitivity is adequate in a dosimetric mode that allows periodic monitoring of system atmospheres. Modeling studies were performed to direct the design of the sensor probe for optimized dimensions and to allow simultaneous monitoring of several constituents with a single sensor fiber. Testing of the system demonstrates the ability to detect 70mTorr partial pressures of H{sub 2} using this technique and <280 {micro}Torr partial pressures of H{sub 2}S. In addition, a multiple sensor fiber has been demonstrated that allows a single fiber to measure H{sub 2}, H{sub 2}S, and H{sub 2}O without changing the fiber or the analytical system.

Thornberg, Steven Michael; White, Michael I.; Rumpf, Arthur Norman; Pfeifer, Kent Bryant

2009-10-01

237

Directed gas-phase formation of the ethynylsulfidoboron molecule.  

PubMed

As a member of the organo sulfidoboron (RBS) family, the hitherto elusive ethynylsulfidoboron molecule (HCCBS) has been formed via the bimolecular reaction of the boron monosulfide radical (BS) with acetylene (C2H2) under single collision conditions in the gas phase, exploiting the crossed molecular beams technique. The reaction mechanism follows indirect dynamics via a barrierless addition of the boron monosulfide radical with its boron atom to the carbon atom of the acetylene molecule, leading to the trans-HCCHBS intermediate. As predicted by ab initio electronic structure calculations, the initial collision complex either isomerizes to its cis-form or undergoes a hydrogen atom migration to form H2CCBS. The cis-HCCHBS intermediate either isomerizes via hydrogen atom shift from the carbon to the boron atom, leading to the HCCBHS isomer, or decomposes to ethynylsulfidoboron (HCCBS). Both H2CCBS and HCCBHS intermediates were predicted to fragment to ethynylsulfidoboron via atomic hydrogen losses. Statistical (RRKM) calculations report yields to form the ethynylsulfidoboron molecule from cis-HCCHBS, H2CCBS, and HCCBHS to be 21%, 7%, and 72%, respectively, under current experimental conditions. Our findings open up an unconventional path to access the previously obscure class of organo sulfidoboron molecules, which are difficult to access through "classical" formation. PMID:24842647

Yang, Tao; Parker, Dorian S N; Dangi, Beni B; Kaiser, Ralf I; Stranges, Domenico; Su, Yuan-Hsiang; Chen, Si-Ying; Chang, Agnes H H; Mebel, Alexander M

2014-06-11

238

Gas Phase Dissociation Behavior of Acyl-Arginine Peptides  

PubMed Central

The gas phase dissociation behavior of peptides containing acyl-arginine residues is investigated. These acylations are generated via a combination of ion/ion reactions between arginine-containing peptides and N-hydroxysuccinimide (NHS) esters and subsequent tandem mass spectrometry (MS/MS). Three main dissociation pathways of acylated arginine, labeled Paths 1-3, have been identified and are dependent on the acyl groups. Path 1 involves the acyl-arginine undergoing deguanidination, resulting in the loss of the acyl group and dissociation of the guanidine to generate an ornithine residue. This pathway generates selective cleavage sites based on the recently discussed “ornithine effect”. Path 2 involves the coordinated losses of H2O and NH3 from the acyl-arginine side chain while maintaining the acylation. We propose that Path 2 is initiated via cyclization of the ?-nitrogen of arginine and the C-terminal carbonyl carbon, resulting in rapid rearrangement from the acyl-arginine side chain and the neutral losses. Path 3 occurs when the acyl group contains ?-hydrogens and is observed as a rearrangement to regenerate unmodified arginine while the acylation is lost as a ketene. PMID:24465154

McGee, William M.; McLuckey, Scott A.

2013-01-01

239

CHAOS II: Gas-Phase Abundances in NGC 5194  

E-print Network

We have observed NGC5194 (M51a) as part of the CHemical Abundances of Spirals (CHAOS) project. Using the Multi Object Double Spectrographs (MODS) on the Large Binocular Telescope (LBT) we are able to measure one or more of the temperature-sensitive auroral lines ([O III] 4363, [N II] 5755, [S III] 6312) and thus measure "direct" gas-phase abundances in 29 individual HII regions. [O III] 4363 is only detected in two HII regions both of which show indications of excitation by shocks. We compare our data to previous direct abundances measured in NGC5194 and find excellent agreement for all but one region (Delta[log(O/H)] ~ 0.04). We find no evidence of trends in Ar/O, Ne/O, or S/O within NGC5194 or compared to other galaxies. We find modest negative gradients in both O/H and N/O with very little scatter (sigma = -0.62) suggests secondary nitrogen production is responsible for a significantly larger fraction of nitrogen (e.g., factor of 8-10) relative to primary production mechanisms than predicted by theoretica...

Croxall, Kevin V; Berg, Danielle; Skillman, Evan D; Moustakas, John

2015-01-01

240

Nuclear symmetry energy effects on liquid-gas phase transition in hot asymmetric nuclear matter  

E-print Network

The liquid-gas phase transition in hot asymmetric nuclear matter is investigated within relativistic mean-field model using the density dependence of nuclear symmetry energy constrained from the measured neutron skin thickness of finite nuclei. We find symmetry energy has a significant influence on several features of liquid-gas phase transition. The boundary and area of the liquid-gas coexistence region, the maximal isospin asymmetry and the critical values of pressure and isospin asymmetry all of which systematically increase with increasing softness in the density dependence of symmetry energy. The critical temperature below which the liquid-gas mixed phase exists is found higher for a softer symmetry energy.

Bharat K. Sharma; Subrata Pal

2010-01-14

241

A united model for predicting pressure wave speeds in oil and gas two-phase pipeflows  

Microsoft Academic Search

A pressure wave, caused by unsteady operations such as a shutdown or restart, pigging, slug flow or input flow rate transient changes during an oil–gas pipeline transmission, could cause a safety hazard to the whole pipeline system. Because of the compressibility of the gas phase, the changes of interface between the gas and liquid, the momentum and energy transfer between

Xiao-Xuan Xu; Jing Gong

2008-01-01

242

GUIDE TO THE DATA SHEETS 1. Gas-Phase Reactions  

E-print Network

/gas chromatographic HPLC - high-performance liquid chromatography IR - infrared LIF - laser induced fluorescence LMR photolysis FTIR - Fourier transform infrared FTS - Fourier transform spectroscopy GC - gas chromatography spectroscopy UV - ultraviolet UVA - ultraviolet absorption VUVA - vacuum ultraviolet absorption

Cambridge, University of

243

Microfabricated gas chromatograph for rapid, trace-level determinations of gas-phase explosive marker compounds.  

PubMed

A prototype microfabricated gas chromatograph (?GC) adapted specifically for the rapid determination of selected gas-phase marker compounds of the explosive 2,4,6-trinitrotoluene (TNT) at sub-parts-per-billion (

Collin, William R; Serrano, Gustavo; Wright, Lindsay K; Chang, Hungwei; Nuñovero, Nicolás; Zellers, Edward T

2014-01-01

244

Pressure drop, heat transfer, critical heat flux, and flow stability of two-phase flow boiling of water and ethylene glycol/water mixtures - final report for project "Efficent cooling in engines with nucleate boiling."  

SciTech Connect

Because of its order-of-magnitude higher heat transfer rates, there is interest in using controllable two-phase nucleate boiling instead of conventional single-phase forced convection in vehicular cooling systems to remove ever increasing heat loads and to eliminate potential hot spots in engines. However, the fundamental understanding of flow boiling mechanisms of a 50/50 ethylene glycol/water mixture under engineering application conditions is still limited. In addition, it is impractical to precisely maintain the volume concentration ratio of the ethylene glycol/water mixture coolant at 50/50. Therefore, any investigation into engine coolant characteristics should include a range of volume concentration ratios around the nominal 50/50 mark. In this study, the forced convective boiling heat transfer of distilled water and ethylene glycol/water mixtures with volume concentration ratios of 40/60, 50/50, and 60/40 in a 2.98-mm-inner-diameter circular tube has been investigated in both the horizontal flow and the vertical flow. The two-phase pressure drop, the forced convective boiling heat transfer coefficient, and the critical heat flux of the test fluids were determined experimentally over a range of the mass flux, the vapor mass quality, and the inlet subcooling through a new boiling data reduction procedure that allowed the analytical calculation of the fluid boiling temperatures along the experimental test section by applying the ideal mixture assumption and the equilibrium assumption along with Raoult's law. Based on the experimental data, predictive methods for the two-phase pressure drop, the forced convective boiling heat transfer coefficient, and the critical heat flux under engine application conditions were developed. The results summarized in this final project report provide the necessary information for designing and implementing nucleate-boiling vehicular cooling systems.

Yu, W.; France, D. M.; Routbort, J. L. (Energy Systems)

2011-01-19

245

Fragile-to-fragile liquid transition at Tg and stable-glass phase nucleation rate maximum at the Kauzmann temperature TK  

NASA Astrophysics Data System (ADS)

An undercooled liquid is unstable. The driving force of the glass transition at Tg is a change of the undercooled-liquid Gibbs free energy. The classical Gibbs free energy change for a crystal formation is completed including an enthalpy saving. The crystal growth critical nucleus is used as a probe to observe the Laplace pressure change ?p accompanying the enthalpy change -Vm×?p at Tg where Vm is the molar volume. A stable glass-liquid transition model predicts the specific heat jump of fragile liquids at T?Tg, the Kauzmann temperature TK where the liquid entropy excess with regard to crystal goes to zero, the equilibrium enthalpy between TK and Tg, the maximum nucleation rate at TK of superclusters containing magic atom numbers, and the equilibrium latent heats at Tg and TK. Strong-to-fragile and strong-to-strong liquid transitions at Tg are also described and all their thermodynamic parameters are determined from their specific heat jumps. The existence of fragile liquids quenched in the amorphous state, which do not undergo liquid-liquid transition during heating preceding their crystallization, is predicted. Long ageing times leading to the formation at TK of a stable glass composed of superclusters containing up to 147 atom, touching and interpenetrating, are evaluated from nucleation rates. A fragile-to-fragile liquid transition occurs at Tg without stable-glass formation while a strong glass is stable after transition.

Tournier, Robert F.

2014-12-01

246

DROPLET PHASE (HETEROGENEOUS) AND GAS PHASE (HOMOGENEOUS) CONTRIBUTIONS TO SECONDARY AMBIENT AEROSOL FORMATION AS FUNCTIONS OF RELATIVE HUMIDITY  

EPA Science Inventory

In previous publications (McMurry and Wilson, 1982; McMurry et al., 1981), techniques for determining the relative contributions of gas phase and liquid phase reactions to secondary ambient aerosol formation have been described. In this paper these methods are applied to more rec...

247

Capillary effects on gas hydrate three-phase stability in marine sediments  

NASA Astrophysics Data System (ADS)

We study the three-phase (Liquid + Gas + Hydrate) stability of the methane hydrate system in marine sediments by considering the capillary effects on both hydrate and free gas phases. The aqueous CH4 solubilities required for forming hydrate (L+H) and free gas (L+G) in different pore sizes can be met in a three-phase zone. The top of the three-phase zone shifts upward in sediments as the water depth increases and the mean pore size decreases. The thickness of the three-phase zone increases as the pore size distribution widens. The top of the three-phase zone can either overlie the three-phase stability depth at deepwater Blake Ridge or underlie the three-phase stability depth at Hydrate Ridge in shallow water. Our model prediction is compatible with worldwide observations that the bottom-simulating reflector is systematically shifted upward relative to the bulk equilibrium depth as water depth (pressure) is increased. The gas hydrate and free gas saturations of the three-phase zone at Blake Ridge Comparison of the globally compiled BSR temperatures with the three-phase equilibrium curves for the systems of pure CH4 + 3.5 wt.% seawater (solid line) and pure CH4 + 2.0 wt.% seawater (dotted line). The discrepancies between the observed BSR temperature and the calculated three-phase temperature are systematically larger in deep water than in shallow water.

Liu, X.; Flemings, P. B.

2013-12-01

248

Gas-phase postderivatization following solid-phase microextraction for determining acidic herbicides in water.  

PubMed

This study analyzes acidic herbicides from an aqueous sample by developing a methylated postderivatization on the fiber following solid-phase microextration (SPME) with diazomethane gas procedure combined with GC/MS. Analysis results indicate that a silica fiber coated with polyacrylate (PA) yields a higher extraction efficiency than that obtained with poly(dimethylsiloxane) (PDMS) using the SPME technique. Detection limits are achieved at the level of 10-30 ng/L. Linearity is obtained over a wide range, with precision below 12% RSD. In addition, the significant reduction in extraction efficiency is attributed to the concentration of humic acids exceeding 5 mg/L. Various degradation compounds of acidic herbicides in basic solution are also detected, including 2,4-dichlorophenol, 2,4,5-trichlorophenol, 4-chloro-3-methylphenol, pentachlorinated biphenyl, and tetrachlorinated biphenyl. Moreover, the amount of pentachlorinated biphenyl and tetrachlorinated biphenyl increases over time. PMID:9599589

Lee, M R; Lee, R J; Lin, Y W; Chen, C M; Hwang, B H

1998-05-01

249

Gas-phase interactions of organotin compounds with glycine.  

PubMed

Gas-phase interactions of organotins with glycine have been studied by combining mass spectrometry experiments and quantum calculations. Positive-ion electrospray spectra show that the interaction of di- and tri-organotins with glycine results in the formation of [(R)2Sn(Gly)-H](+) and [(R)3Sn(Gly)](+) ions, respectively. Di-organotin complexes appear much more reactive than those involving tri-organotins. (MS/MS) spectra of the [(R)3Sn(Gly)](+) ions are indeed simple and only show elimination of intact glycine, generating the [(R)3Sn](+) carbocation. On the other hand, MS/MS spectra of [(R)2Sn(Gly)-H](+) complexes are characterized by numerous fragmentation processes. Six of them, associated with elimination of H2O, CO, H2O?+?CO and formation of [(R)2SnOH](+) (-57?u),[(R)2SnNH2](+) (-58?u) and [(R)2SnH](+) (-73?u), are systematically observed. Use of labeled glycines notably concludes that the hydrogen atoms eliminated in water and H2O?+?CO are labile hydrogens. A similar conclusion can be made for hydrogens of [(R2)SnOH](+) and [(R2)SnNH2](+) ions. Interestingly, formation [(R)2SnH](+) ions is characterized by a migration of one the ? hydrogen of glycine onto the metallic center. Finally, several dissociation routes are observed and are characteristic of a given organic substituent. Calculations indicated that the interaction between organotins and glycine is mostly electrostatic. For [(R)2Sn(Gly)-H](+) complexes, a preferable bidentate interaction of the type ?(2)-O,NH2 is observed, similar to that encountered for other metal ions. [(R)3Sn](+) ions strongly stabilize the zwitterionic form of glycine, which is practically degenerate with respect to neutral glycine. In addition, the interconversion between both forms is almost barrierless. Suitable mechanisms are proposed in order to account for the most relevant fragmentation processes. PMID:23832935

Latrous, Latifa; Tortajada, Jeanine; Haldys, Violette; Léon, Emmanuelle; Correia, Catarina; Salpin, Jean-Yves

2013-07-01

250

Gas-Phase Combustion Synthesis of Aluminum Nitride Powder  

NASA Technical Reports Server (NTRS)

Due to its combined properties of high electrical resistivity and high thermal conductivity aluminum nitride (AlN) is a highly desirable material for electronics applications. Methods are being sought for synthesis of unagglomerated, nanometer-sized powders of this material, prepared in such a way that they can be consolidated into solid compacts having minimal oxygen content. A procedure for synthesizing these powders through gas-phase combustion is described. This novel approach involves reacting AlCl3, NH3, and Na vapors. Equilibrium thermodynamic calculations show that 100% yields can be obtained for these reactants with the products being AlN, NaCl, and H2. The NaCl by-product is used to coat the AlN particles in situ. The coating allows for control of AlN agglomeration and protects the powders from hydrolysis during post-flame handling. On the basis of thermodynamic and kinetic considerations, two different approaches were employed to produce the powder, in co-flow diffusion flame configurations. In the first approach, the three reactants were supplied in separate streams. In the second, the AlCl3 and NH3 were premixed with HCl and then reacted with Na vapor. X-ray diffraction (XRD) spectra of as-produced powders show only NaCl for the first case and NaCl and AlN for the second. After annealing at 775 C tinder dynamic vacuum, the salt was removed and XRD spectra of powders from both approaches show only AlN. Aluminum metal was also produced in the co-flow flame by reacting AlCl3 with Na. XRD spectra of as-produced powders show the products to be only NaCl and elemental aluminum.

Axelbaum, R. L.; Lottes, C. R.; Huertas, J. I.; Rosen, L. J.

1996-01-01

251

IV-VI semiconductor lasers for gas phase biomarker detection  

NASA Astrophysics Data System (ADS)

A promising absorption spectroscopy application for mid-IR lasers is exhaled breath analysis where sensitive, selective, and speedy measurement of small gas phase biomarker molecules can be used to diagnose disease and monitor therapies. Many molecules such as nitric oxide, ethane, formaldehyde, acetaldehyde, acetone, carbonyl sulfide, and carbon disulfide have been connected to diseases or conditions such as asthma, oxidative stress, breast cancer, lung cancer, diabetes, organ transplant rejection, and schizophrenia. Measuring these and other, yet to be discovered, biomarker molecules in exhaled breath with mid-IR lasers offers great potential for improving health care since such tests are non-invasive, real-time, and do not require expensive consumables or chemical reagents. Motivated by these potential benefits, mid-IR laser spectrometers equipped with presently available cryogenically-cooled IV-VI lasers mounted in compact Stirling coolers have been developed for clinical research applications. This paper will begin with a description of the development of mid-IR laser instruments and their use in the largest known exhaled breath clinical study ever performed. It will then shift to a description of recent work on the development of new IV-VI semiconductor quantum well materials and laser fabrication methods that offer the promise of low power consumption (i.e. efficient) continuous wave emission at room temperature. Taken together, the demonstration of compelling clinical applications with large market opportunities and the clear identification of a viable pathway to develop low cost mid-IR laser instrumentation can create a renewed focus for future research and development efforts within the mid-IR materials and devices area.

McCann, Patrick; Namjou, Khosrow; Roller, Chad; McMillen, Gina; Kamat, Pratyuma

2007-09-01

252

Gas-Phase Combustion Synthesis of Nonoxide Nanoparticles in Microgravity  

NASA Technical Reports Server (NTRS)

Gas-phase combustion synthesis is a promising process for creating nanoparticles for the growing nanostructure materials industry. The challenges that must be addressed are controlling particle size, preventing hard agglomerates, maintaining purity, and, if nonoxides are synthesized, protecting the particles from oxidation and/or hydrolysis during post-processing. Sodium-halide Flame Encapsulation (SFE) is a unique methodology for producing nonoxide nanoparticles that addresses these challenges. This flame synthesis process incorporates sodium and metal-halide chemistry, resulting in nanoparticles that are encapsulated in salt during the early stages of their growth in the flame. Salt encapsulation has been shown to allow control of particle size and morphology, while serving as an effective protective coating for preserving the purity of the core particles. Metals and compounds that have been produced using this technology include Al, W, Ti, TiB2, AlN, and composites of W-Ti and Al-AlN. Oxygen content in SFE synthesized nano- AlN has been measured by neutron activation analysis to be as low as 0.54wt.%, as compared to over 5wt.% for unprotected AlN of comparable size. The overall objective of this work is to study the SFE process and nano-encapsulation so that they can be used to produce novel and superior materials. SFE experiments in microgravity allow the study of flame and particle dynamics without the influence of buoyancy forces. Spherical sodium-halide flames are produced in microgravity by ejecting the halide from a spherical porous burner into a quiescent atmosphere of sodium vapor and argon. Experiments are performed in the 2.2 sec Drop Tower at the NASA-Glenn Research Center. Numerical models of the flame and particle dynamics were developed and are compared with the experimental results.

Axelbaum, R. L.; Kumfer, B. M.; Sun, Z.; Chao, B. H.

2001-01-01

253

Infrared spectroscopy of ionized corannulene in the gas phase  

NASA Astrophysics Data System (ADS)

The gas-phase infrared spectra of radical cationic and protonated corannulene were recorded by infrared multiple-photon dissociation (IRMPD) spectroscopy using the IR free electron laser for infrared experiments. Electrospray ionization was used to generate protonated corannulene and an IRMPD spectrum was recorded in a Fourier-transform ion cyclotron resonance mass spectrometer monitoring H-loss as a function of IR frequency. The radical cation was produced by 193-nm UV photoionization of the vapor of corannulene in a 3D quadrupole trap and IR irradiation produces H, H2, and C2Hx losses. Summing the spectral response of the three fragmentation channels yields the IRMPD spectrum of the radical cation. The spectra were analyzed with the aid of quantum-chemical calculations carried out at various levels of theory. The good agreement of theoretical and experimental spectra for protonated corannulene indicates that protonation occurs on one of the peripheral C-atoms, forming an sp3 hybridized carbon. The spectrum of the radical cation was examined taking into account distortions of the C5v geometry induced by the Jahn-Teller effect as a consequence of the degenerate 2E1 ground electronic state. As indicated by the calculations, the five equivalent Cs minima are separated by marginal barriers, giving rise to a dynamically distorted system. Although in general the character of the various computed vibrational bands appears to be in order, only a qualitative match to the experimental spectrum is found. Along with a general redshift of the calculated frequencies, the IR intensities of modes in the 1000-1250 cm-1 region show the largest discrepancy with the harmonic predictions. In addition to CH "in-plane" bending vibrations, these modes also exhibit substantial deformation of the pentagonal inner ring, which may relate directly to the vibronic interaction in the radical cation.

Galué, Héctor Alvaro; Rice, Corey A.; Steill, Jeffrey D.; Oomens, Jos

2011-02-01

254

Gas-phase production of single-walled carbon nanotubes from carbon monoxide: a review of the hipco process  

NASA Technical Reports Server (NTRS)

The latest process for producing large quantities of single-walled carbon nanotubes (SWNTs) to emerge from the Rice University, dubbed HiPco, is living up to its promise. The current production rates approach 450 mg/h (or 10 g/day), and nanotubes typically have no more than 7 mol % of iron impurities. Second-generation HiPco apparatus can run continuously for 7-10 days at a time. In the HiPco process nanotubes grow in high-pressure, high-temperature flowing CO on catalytic clusters of iron. Catalyst is formed in situ by thermal decomposition of iron pentacarbonyl, which is delivered intact within a cold CO flow and then rapidly mixed with hot CO in the reaction zone. Upon heating, the Fe(CO)5 decomposes into atoms that condense into larger clusters. SWNTs nucleate and grow on these particles in the gas phase via CO disproportionation: CO + CO --> CO2 + C (SWNT), catalyzed by the Fe surface. The concentration of CO2 produced in this reaction is equal to that of carbon and can therefore serve as a useful real-time feedback parameter. It was used to study and optimize SWNT production as a function of temperature, pressure, and Fe(CO)5 concentration. The results of the parametric study are in agreement with current understanding of the nanotube formation mechanism.

Nikolaev, Pavel

2004-01-01

255

Nonlinear Acoustical Assessment of Precipitate Nucleation  

NASA Technical Reports Server (NTRS)

The purpose of the present work is to show that measurements of the acoustic nonlinearity parameter in heat treatable alloys as a function of heat treatment time can provide quantitative information about the kinetics of precipitate nucleation and growth in such alloys. Generally, information on the kinetics of phase transformations is obtained from time-sequenced electron microscopical examination and differential scanning microcalorimetry. The present nonlinear acoustical assessment of precipitation kinetics is based on the development of a multiparameter analytical model of the effects on the nonlinearity parameter of precipitate nucleation and growth in the alloy system. A nonlinear curve fit of the model equation to the experimental data is then used to extract the kinetic parameters related to the nucleation and growth of the targeted precipitate. The analytical model and curve fit is applied to the assessment of S' precipitation in aluminum alloy 2024 during artificial aging from the T4 to the T6 temper.

Cantrell, John H.; Yost, William T.

2004-01-01

256

Homogeneous crystal nucleation in binary metallic melts  

NASA Technical Reports Server (NTRS)

A method for calculating the homogeneous crystal nucleation frequency in binary metallic melts is developed. The free energy of crystallization is derived from regular solution models for the liquid and solid and is used, together with model-based estimates of the interfacial tension, to calculate the nucleation frequency from the classical theory. The method can account for the composition dependence of the maximum undercooling observed in a number of experiments on small droplet dispersions. It can also be used to calculate the driving force for crystal growth and to obtain more precise estimates of the homogeneous crystal nucleation frequency in glass-forming alloys. This method, although approximate, is simple to apply, and requires only knowledge of the phase diagram and a few readily available thermodynamic quantities as input data.

Thompson, C. V.; Spaepen, F.

1983-01-01

257

Three-phase measurements of oil and gas trapping in sand packs  

NASA Astrophysics Data System (ADS)

We measure the trapped saturations of oil and gas as a function of initial saturation in water-wet sand packs. We start with a water-saturated column and inject octane (oil), while water and oil are produced from the bottom. Once water production has ceased, air (gas) then enters from the top, allowing oil and gas to drain under gravity for different times. Finally water is then injected from the bottom to trap both oil and gas. The columns are sliced and the fluids analyzed using gas chromatography. We find that for high initial gas saturations more gas can be trapped in the presence of oil than in a two-phase (gas/water) system. The residual gas saturation can be over 20% compared to 14% in two-phase flow [Al Mansoori SK, Iglauer S, Pentland CH, Bijeljic B, Blunt MJ. Measurements of non-wetting phase trapping applied to carbon dioxide storage. Energy Procedia 2009;1(1):3173-80]. This is unlike previous measurements on consolidated media, where the trapped gas saturation is either similar or lower to that reached in an equivalent two-phase experiment. For lower initial gas saturation, the amount of trapping follows the initial-residual trend seen in two-phase experiments. The amount of oil trapped is insensitive to initial gas saturation or the amount of gas that is trapped, again in contrast to measurements on consolidated media. More oil is trapped than would be predicted from an equivalent two-phase (oil/water) system, although the trapped saturation is never larger than the maximum reached in two-phase flow (around 11%) [Pentland CH, Al Mansoori SK, Iglauer S, Bijeljic B, Blunt MJ. Measurement of non-wetting phase trapping in sand packs. In: SPE 115697, proceedings of the SPE annual technical conference and exhibition, Denver, Colorado, USA; 21-24 September 2008]. These initially surprising results are explained in the context of oil layer stability and the competition between snap-off and piston-like advance. In two-phase systems, displacement is principally by cooperative piston-like advance with relatively little trapping, whereas in consolidated media snap-off is generally more significant. However, oil layer collapse events during three-phase waterflooding rapidly trap the oil which acts as a barrier to direct water/gas displacement, except by snap-off, leading to enhanced gas trapping.

Al Mansoori, Saleh K.; Iglauer, Stefan; Pentland, Christopher H.; Blunt, Martin J.

2009-10-01

258

Laboratory Investigations of Titan Haze Formation: Characterization of Gas Phase and Particle Phase Nitrogen  

NASA Astrophysics Data System (ADS)

Prior to the arrival of the Cassini-Huygens spacecraft, aerosol production in Titan’s atmosphere was believed to begin in the stratosphere where chemical processes are predominantly initiated by far ultraviolet (FUV) radiation. However, the discovery of very heavy ions, coupled with Cassini Ultraviolet Imaging Spectrograph (UVIS) occultation measurements that show haze absorption up to 1000 km altitude (Liang et al., 2007), indicates that haze formation initiates in the thermosphere. The energy environment of the thermosphere is significantly different from the stratosphere; in particular there is a greater flux of extreme ultraviolet (EUV) photons and energetic particles available to initiate chemical reactions, including the destruction of N2, in the upper atmosphere. The discovery of previously unpredicted nitrogen species in measurements of Titan’s atmosphere by the Cassini Ion and Neutral Mass Spectrometer (INMS) indicates that nitrogen participates in the chemistry to a much greater extent than was appreciated before Cassini (Vuitton et al., 2007). Additionally, measurements obtained by the Aerosol Collector Pyrolyzer (ACP) carried by Huygens to Titan’s surface may indicate that Titan’s aerosols contain significant amounts of nitrogen (Israël et al., 2005, 2006). The degree of nitrogen incorporation in the haze particles is important for understanding the diversity of molecules that may be present in Titan’s atmosphere and on its surface. We have conducted a series of Titan atmosphere simulation experiments using either spark discharge (tesla coil) or FUV photons (deuterium lamp) to initiate chemistry in CH4/N2 gas mixtures ranging from 0.01% CH4/99.99% N2 to 10% CH4/90% N2. We obtained in situ measurements using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) to measure the particle composition as a function of particle size and a proton-transfer ion-trap mass spectrometer (PIT-MS) to measure the composition of gas phase products. These two techniques allow us to investigate the effect of energy source and initial CH4 concentration on the degree of nitrogen incorporation in both the gas and solid phase products.

Horst, Sarah; Yoon, Heidi; Li, Rui; deGouw, Joost; Tolbert, Margaret

2014-11-01

259

Molecular Dynamics Simulation of Homogeneous Crystal Nucleation in Polyethylene  

E-print Network

Using a realistic united-atom force field, molecular dynamics simulations were performed to study homogeneous nucleation of the crystal phase at about 30% supercooling from the melts of n-pentacontahectane (C150) and a ...

Yi, Peng

260

Enhancement of gas-phase diffusion in the presence of liquid  

NASA Astrophysics Data System (ADS)

Gas diffusion in porous media occurs in both the gas and liquid phases. In many instances, gas diffusion in the liquid phase is ignored. However, under many conditions, gas diffusion in the liquid phase may be more important than gas diffusion in the gas phase. Two different cases will be examined in this work. The first case is a continuous liquid path between the gas concentrations of interest modeled after Jury et al. (1984). The second case is the situation at low liquid saturation where liquid islands exist. For the first case, Jury's model can be rewritten as a ratio of the total gas diffusion in the gas and liquid phases to that just in the gas phase. The liquid diffusion coefficient is approximately 10-4 times the gas diffusion coefficient consistent with Jury et al. (1984). The ratio of total diffusion to gas-phase diffusion is then only a function of Henry's constant and the liquid saturation. For higher values of Henry's constant, such as for CO2 and O2, the effect of diffusion in the liquid phase is small except at high liquid saturations. For small values of Henry's constant, such as for some VOCs and explosive compounds, diffusion in the liquid phase dominates for low and moderate liquid saturation values. The second case is the enhancement of diffusion caused by liquid islands at low liquid saturation. Enhanced vapor diffusion across liquid islands has been observed and modeled by Webb and Ho (1999), where condensation and evaporation occur on opposite ends of the liquid island. Vapor diffusion enhancement of up to a factor of 10 has been observed. Similarly, gas can diffuse through the liquid island. For high values of Henry's constant, gas diffusion through liquid islands is negligible and can be ignored. For small values of Henry's constant, diffusion through liquid islands may be much greater than diffusion through gas, so the rate is enhanced. The work was sponsored by the Geneva International Center for Humanitarian Demining (GICHD) under the direction of Havard Bach. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

Webb, S.; Angert, A.

2003-04-01

261

The gas-phase thermal chemistry of tetralin and related model systems  

SciTech Connect

The thesis is divided into 5 papers: gas-phase thermal decomposition of tetralin; flash vacuum pyrolysis of 3-benzocycloheptenone and 1,3, 4,5-tetrahydro-2-benzothiepin-2,2-dioxide (model systems for gas-phase pyrolysis of tetralin); high-temperature gas-phase reactions of o-allylbenzyl radicals generated by flash vacuum pyrolysis of is(o-allylbenzyl) oxalate; flash vacuum pyrolysis of 1,4-diphenylbutane; and flash vacuum pyrolysis of o-allyltoluene, o-(3-butenyl)toluene and o-(pentenyl)toluene were also used.

Malandra, J.

1993-05-01

262

Dynamics of the gas phase in a fuel-rod assembly simulator with a spacing grid  

NASA Astrophysics Data System (ADS)

An experimental study of two-phase flow in a model of assembly of 37 fuel rods in a triangular arrangement was performed. Measurements were performed with local gas supply through a unit nozzle. Distributions of the local void fraction were obtained at various values of angular coordinate and distance from a spacing grid. It was shown that most of the gas phase moves in a space produced by the walls of three nearby rods. A significant increase of gas phase concentration takes place in the flow region just after the grid.

Kashinsky, O. N.; Lobanov, P. D.; Kurdyumov, A. S.; Pribaturin, N. A.; Volkov, S. E.

2013-07-01

263

Gas phase dispersion in compost as a function of different water contents and air flow rates  

NASA Astrophysics Data System (ADS)

Gas phase dispersion in a natural porous medium (yard waste compost) was investigated as a function of gas flow velocity and compost volumetric water content using oxygen and nitrogen as tracer gases. The compost was chosen because it has a very wide water content range and because it represents a wide range of porous media, including soils and biofilter media. Column breakthrough curves for oxygen and nitrogen were measured at relatively low pore gas velocities, corresponding to those observed in for instance soil vapor extraction systems or biofilters for air cleaning at biogas plants or composting facilities. Total gas mechanical dispersion-molecular diffusion coefficients were fitted from the breakthrough curves using a one-dimensional numerical solution to the advection-dispersion equation and used to determine gas dispersivities at different volumetric gas contents. The results showed that gas mechanical dispersion dominated over molecular diffusion with mechanical dispersion for all water contents and pore gas velocities investigated. Importance of mechanical dispersion increased with increasing pore gas velocity and compost water content. The results further showed that gas dispersivity was relatively constant at high values of compost gas-filled porosity but increased with decreasing gas-filled porosity at lower values of gas-filled porosity. Results finally showed that measurement uncertainty in gas dispersivity is generally highest at low values of pore gas velocity.

Sharma, Prabhakar; Poulsen, Tjalfe G.

2009-07-01

264

Detection methods for atoms and radicals in the gas phase  

NASA Astrophysics Data System (ADS)

This report lists atoms and free radicals in the gas phase which are of interest for environmental and flame chemistry and have been detected directly. The detection methods which have been used are discussed with respect to their range of application, specificity and sensitivity. In table 1, detection methods for the five atoms of group IV (C, Si, Ge, Sn, Pb) and about 60 radicals containing at least one atom of group IV are summarized (CH, Cd, Cf, CC1, CBr, Cn, Cs, CSe, CH2, CD2, Chf, Cdf, CHC1, CHBr, CF2, CC12, CBr2, CFC1, CFBr, CH3, CD3, CF3, CH2F, CH2C1, CH2Br, CHF2, CHC12, CHBr2, Hco, Fco, CH30, CD30, CH2OH, CH3S, Nco, CH4N, CH302, CF302; C2, C2N, C2H, C20, C2HO, C2H3, C2F3, C2H5, C2HsO, C2H4OH, CH3CO, CD3CO, C2H3O, C2H502, CH3COO2, C2H4N, C2H6N, C3; Si, SiF, SiF2, SiO, SiC, Si2; Ge, GeC, GeO, GeF, GeF2, GeCl2, Sn, SnF, SnO, SnF2, Pb, PbF, PbF2, PbO, PbS). In table 2 detection methods for about 25 other atoms and 60 radicals are listed: (H, D, O, O2, Oh, Od, HO2, DO2, F, Ci, Br, I, Fo, Cio, BrO, Io, FO2, C1O2, Li, Na, K, Rb, Cs, N, N3, Nh, Nd, Nf, Nci, NBr, NH2, ND2, Nhd, Nhf, NF2, NC12, N2H3, No, NO2, NO3, Hno, Dno, P, Ph, Pd, Pf, Pci, PH2, PD2, PF2, Po, As, AsO, AsS, Sb, Bi, S, S2, Sh, Sd, Sf, SF2, So, Hso, Dso, Sn, Se, Te, Se2, SeH, SeD, SeF, SeO, SeS, SeN, TeH, TeO, Bh, BH2, Bo, Bn, B02, Cd, Hg, UF5). The tables also cite some recent kinetic applications of the various methods.

Hack, W.

265

An investigation into the flow behavior of a single phase gas system and a two phase gas/liquid system in normal gravity with nonuniform heating from above  

NASA Technical Reports Server (NTRS)

The fluid behavior in normal gravity of a single phase gas system and a two phase gas/liquid system in an enclosed circular cylinder heated suddenly and nonuniformly from above was investigated. Flow visualization was used to obtain qualitative data on both systems. The use of thermochromatic liquid crystal particles as liquid phase flow tracers was evaluated as a possible means of simultaneously gathering both flow pattern and temperature gradient data for the two phase system. The results of the flow visualization experiments performed on both systems can be used to gain a better understanding of the behavior of such systems in a reduced gravity environment and aid in the verification of a numerical model of the system.

Disimile, Peter J.; Heist, Timothy J.

1990-01-01

266

Phase Transition of Methane Gas Hydrate and Response of Marine Gas Hydrate Systems to Environmental Changes  

Microsoft Academic Search

Gas hydrates, which contain mostly methane as the gas component in marine sediment, are stable under relatively high pressure and low temperature conditions such as those found along continental margins and permafrost regions. Its stability is mostly controlled by in-situ pressure, temperature and salinity of pore fluid. Environmentally introduced changes in pressure and temperature can affect the stability of gas

W. Xu

2003-01-01

267

Volumes of critical bubbles from the nucleation theorem  

NASA Astrophysics Data System (ADS)

A corollary of the nucleation theorem due to Kashchiev [Nucleation: Basic Theory with Applications (Butterworth-Heinemann, Oxford, 2000)] allows the volume V* of a critical bubble to be determined from nucleation rate measurements. The original derivation was limited to one-component, ideal gas bubbles with a vapor density much smaller than that of the ambient liquid. Here, an exact result is found for multicomponent, nonideal gas bubbles. Provided a weak density inequality holds, this result reduces to Kashchiev's simple form which thus has a much broader range of applicability than originally expected. Limited applications to droplets are also mentioned, and the utility of the pT,x form of the nucleation theorem as a sum rule is noted.

Wilemski, Gerald

2006-09-01

268

DETERMINATION OF CHLOROETHENES IN ENVIRONMENTAL BIOLOGICAL SAMPLES USING GAS CHROMATOGRAPHY COUPLED WITH SOLID PHASE MICRO EXTRACTION  

EPA Science Inventory

An analytical method has been developed to determine the chloroethene series, tetrachloroethene (PCE), trichloroethene (TCE),cisdichloroethene (cis-DCE) andtransdichloroethene (trans-DCE) in environmental biotreatment studies using gas chromatography coupled with a solid phase mi...

269

Sulfur hexafluoride: Optimal use as a gas-phase, infrared sensitizer  

SciTech Connect

Investigations into the use of sulfur hexafluoride, SF[sub 6], as a gas-phase, infrared photochemical sensitizer have revealed several interesting phenomena. The expedient use of SF[sub 6] can produce an optimal quantity of nitrated product in the gas-phase, laser-induced nitration of cyclopentane. The optimal utilization of sulfur hexafluoride required critical optimization of both frequency and quantity. The results are described herein. 12 refs., 3 figs., 1 tab.

Stanley, A.E.; Ludwick, L.M.; White, D.; Andrews, D.E.; Godbey, S.E. (AMSMI-RD-WS-CM, Redstone Arsenal, AL (United States))

1992-12-01

270

Feature Extraction Method for Gas\\/Liquid Two-Phase Flow Based on Wavelets Transform  

Microsoft Academic Search

Gas\\/liquid two-phase flow system is a complex, nonlinear and dynamic system, therefore is difficult to measure. Basing on the application of electrical resistance tomography (ERT) in gas\\/liquid two-phase flow of vertical pipe, wavelets transform is used to analyses the measured data from ERT system. Furthermore, according to the multi-resolution analysis (MRA), the feature vector of multiple scales wavelet energy that

Meng-Meng Wu; Feng Dong; Guo-Hua Qi

2006-01-01

271

An atmospheric pressure flow reactor: Gas phase kinetics and mechanism in tropospheric conditions without wall effects  

NASA Technical Reports Server (NTRS)

A new type of gas phase flow reactor, designed to permit the study of gas phase reactions near 1 atm of pressure, is described. A general solution to the flow/diffusion/reaction equations describing reactor performance under pseudo-first-order kinetic conditions is presented along with a discussion of critical reactor parameters and reactor limitations. The results of numerical simulations of the reactions of ozone with monomethylhydrazine and hydrazine are discussed, and performance data from a prototype flow reactor are presented.

Koontz, Steven L.; Davis, Dennis D.; Hansen, Merrill

1988-01-01

272

Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species  

SciTech Connect

This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. High-resolution spectroscopy, augmented by theoretical and computational methods, is used to investigate the structure and collision dynamics of chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry. Applications and methods development are equally important experimental components of this work.

Hall,G.E.; Sears, T.J.

2009-04-03

273

Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species  

SciTech Connect

This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

Hall G. E.; Goncharov, V.

2012-05-29

274

Severe slugging in gas-liquid two-phase pipe flow  

Microsoft Academic Search

transportation facilities. In an offshore oil and gas production facility, pipeline-riser systems are required to transport two-phase hydrocarbons from subsurface oil and gas wells to a central production platform. Severe slugs reaching several thousands pipe diameters may occur when transporting gas and liquid in these pipeline-riser systems.\\u000a\\u000aSevere slugging creates potential problems in the platform facilities, e.g. separators, pumps, and

R. Malekzadeh

2012-01-01

275

DEMONSTRATION BULLETIN: GAS-PHASE CHEMICAL REDUCTION - ECO LOGIC INTERNATIONAL, INC.  

EPA Science Inventory

The patented Eco Logic Process employs a gas-phase reduction reaction of hydrogen with organic and chlorinated organic compounds at elevated temperatures to convert aqueous and oily hazardous contaminants into a hydrocarbon-rich gas product. After passing through a scrubber, the ...

276

APPLICATIONS ANALYSIS REPORT: ECO LOGIC INTERNATIONAL GAS-PHASE CHEMICAL REDUCTION PROCESS - THE REACTOR SYSTEM  

EPA Science Inventory

This report details the Superfund Innovative Technology Evaluation of Eco Logic International's gas-phase chemical reduction process, with an emphasis on their Reactor System. he Eco Logic process employees a high temperature reactor filled with hydrogen gas as the means to destr...

277

Carbon Nanotube Stationary Phase in a Microfabricated Column for High-Performance Gas Chromatography  

E-print Network

Chromatography Takashi Nakai* , Jun Okawa, Shuji Takada, Masaki Shuzo* , Junichiro Shiomi, Jean-Jacques Delaunay a microfabricated gas chromatography (GC) column that uses a thin layer of high-quality single- walled carbon useful for high-performance micro-GC. Keywords: Carbon Nanotube, Stationary Phase, Gas Chromatography

Maruyama, Shigeo

278

Microgravity nucleation and particle coagulation experiments support  

NASA Technical Reports Server (NTRS)

Modifications to the nucleation apparatus suggested by our first microgravity flight campaign are complete. These included a complete 'repackaging' of the equipment into three racks along with an improved vapor spout shutter mechanism and additional thermocouples for gas temperature measurements. The 'repackaged' apparatus was used in two KC-135 campaigns: one during the week of June 3, 1991 consisting of two flights with Mg and two with Zn, and another series consisting of three flights with Zn during the week of September 23, 1991. Our effort then was focused on the analysis of these data, including further development of the mathematical models to generate the values of temperature and supersaturation at the observed points of nucleation. The efforts to apply Hale's Scaled Nucleation Theory to our experimental data have met with only limited success, most likely due to still inadequate temperature field determination. Work on the development of a preliminary particle collector system designed to capture particles from the region of nucleation and condensation, as well as from other parts of the chamber, are discussed.

Lilleleht, L. U.; Ferguson, F. T.; Stephens, J. R.

1992-01-01

279

Non-LTE dust nucleation in sub-saturated vapors  

E-print Network

We use the kinetic theory of nucleation to explore the properties of dust nucleation in sub-saturated vapors. Due to radiation losses, the sub-critical clusters have a smaller temperature compared to their vapor. This alters the dynamical balance between attachment and detachment of monomers, allowing for stable nucleation of grains in vapors that are sub-saturated for their temperature. We find this effect particularly important at low densities and in the absence of a strong background radiation field. We find new conditions for stable nucleation in the n-T phase diagram. The nucleation in the non-LTE regions is likely to be at much slower rate than in the super-saturated vapors. We evaluate the nucleation rate, warning the reader that it does depend on poorly substantiated properties of the macro-molecules assumed in the computation. On the other hand, the conditions for nucleation depend only on the properties of the large stable grains and are more robust. We finally point out that this mechanism may be relevant in the early universe as an initial dust pollution mechanism, since once the interstellar medium is polluted with dust, mantle growth is likely to be dominant over non-LTE nucleation in the diffuse medium.

Davide Lazzati

2007-11-09

280

Crystallization and nucleation kinetics in volcanic systems  

NASA Astrophysics Data System (ADS)

The main objective of this experimental study is to constrain and quantitatively model the complex solidification process that transforms a magma in a solid material. Of major interest are crystal nucleation and growth driven by isothermal decompression of hydrous magmas, and comparison with results from more abundant crystal growth/nucleation data obtained in isobaric cooling experiments. This research concerns two different volcanic systems, Pantelleria (peralkaline rhyolite) and Stromboli (basalt), to better understand how crystallization kinetics can affect different magma compositions. For Stromboli volcanic system TZM apparatus has been used to perform decompression runs at Bayerisches Geoinstitut in Bayreuth (DE). As for Pantelleria composition, cooling experiments has been done using IHPV devices at ISTO of Orléans (FR), on the basis of previous phase equilibrium work (Di Carlo et al., 2010). First obtained results for Stromboli case show high rates of nucleation and crystal growth during the initial stages of crystallization which were followed by crystal growth at approximately constant number densities as equilibrium was approached. Shapes of crystals growing in melts are controlled by the kinetics of crystallization and may provide information about the degree of undercooling experienced by batches of magma en route to the surface (Lofgren, 1980). The study of crystallization kinetics through phases growth rates (Couch et al., 2003), together with the calculation of nucleation density and nucleation rates (Hammer et al., 1999) represent a step toward the estimation of the time scales of magmatic processes in volcanic systems and the interpretation of shallow magmatic processes. The results for Stromboli suggest average crystal growth timescales on the order of weeks, but this is complicated by clear evidence that some crystals have experienced repeated periods of both dissolution and growth (Landi et al., 2004).

Agostini, C.; Fortunati, A.; Carroll, M. R.; Scaillet, B.; Landi, P.

2011-12-01

281

Abatement of Gas-Phase Mercury—Recent Developments  

Microsoft Academic Search

Among various pollutants, mercury has a significant impact on the environment, human beings, and wildlife with its different forms, namely, elemental mercury (Hg), oxidized mercury (Hg), and particle-bound mercury (Hgp). Mercury dispersions mainly occur from coal burning, which is the world's major energy source. Among the three forms, Hg and Hgp are relatively easy to remove from the flue gas

Benjaram M. Reddy; Naga Durgasri; Thallada Vinod Kumar; Suresh K. Bhargava

2012-01-01

282

Gas phase dispersion in a small rotary kiln  

SciTech Connect

A study was made of nonideal flow of gas in a rotary kiln reactor. A rotating tube 0.165 m in diameter by 2.17 m long, with internal lifting flights, was operated at room temperature. Rotational speeds from 2.0 to 7.0 rpm, air flow rates from 0.351 to 4.178 m/sup 3//h, and solid contents of 0.0, 5.1, and 15.3% of tube volume were studied. Residence time distribution of the gas was measured by means of the pulse injection technique using a helium tracer. A model was developed based on dispersive flow that exchanges with a deadwater region. Two parameters, a dispersion number describing bulk gas flow and an interchange factor describing exchange between the flow region and the gas trapped in the solids bed, were sufficient to correlate the data, but these parameters are sensitive to experimental error. The model is applicable to analysis of other flow systems, such as packed beds.

Spencer, B.B.

1981-07-01

283

Ceramic stationary gas turbine development. Final report, Phase 1  

SciTech Connect

This report summarizes work performed by Solar Turbines Inc. and its subcontractors during the period September 25, 1992 through April 30, 1993. The objective of the work is to improve the performance of stationary gas turbines in cogeneration through implementation of selected ceramic components.

NONE

1994-09-01

284

NANOMATERIAL SOLUTIONS FOR HOT COAL GAS CLEANUP - PHASE I  

EPA Science Inventory

Integrated gasification combined cycle (IGCC) is a new coal gasification technique that efficiently uses the hot (900-1500°C) generated syngas to power both steam and gas turbines. Due to regulations, this syngas must be free of sulfur and purification is normally carried ...

285

Phase transition or Maxwell's demon in Granular gas?  

Microsoft Academic Search

Dynamics of vibro-fluidised granular gas is investigated experimentally using the transfer of grains from a compartment through a horizontal slit at a given height h . It is demonstrated that the transfer rate j varies linearly with the grain number N in the box when N remains small; however j(N) becomes strongly non linear as soon as the number n

P. Jean; H. Bellenger; P. Burban; L. Ponson; P. Evesque

2005-01-01

286

Partitioning of semivolatile surface-active compounds between bulk, surface and gas phase  

NASA Astrophysics Data System (ADS)

We present a model study demonstrating that surface partitioning of volatile surfactants enhances their uptake by submicron liquid droplets. In submicron-sized droplets, surface partitioning of a surface-active volatile species may significantly decrease its equilibrium partial pressure, thus increasing the total flux of the surfactant from gas phase to aqueous phase. Such uptake of volatile organic species into aqueous aerosols can be followed by aqueous-phase chemistry to form low-volatility secondary organic aerosol material, leading to increased aerosol mass. In the study, we used an air parcel model that includes simplified aqueous- and gas-phase chemistry, condensation/evaporation, and a model of aqueous-phase thermodynamics that takes into account the partitioning of surfactants between the bulk and surface phases. We modeled the uptake and aqueous-phase chemical reactions of methylglyoxal, as it is a moderate surfactant that forms less volatile secondary organic material via aqueous-phase chemical reactions with the hydroxyl radical as well as hydronium and ammonium ions. Our model simulations show an order of magnitude higher uptake of methylglyoxal in aqueous aerosols of cloud condensation nuclei sizes (less than 200 nm in radius) when surface partitioning is taken into account, compared to when surface partitioning is neglected. As a consequence, the production of SOA through the aqueous-phase chemical processing of methylglyoxal is also enhanced, but to a lesser degree, because condensation of the hydroxyl radical from gas phase limits the production.

Romakkaniemi, S.; Kokkola, H.; Smith, J. N.; Prisle, N. L.; Schwier, A. N.; McNeill, V. F.; Laaksonen, A.

2011-02-01

287

ANALYSIS OF A GAS-PHASE PARTITIONING TRACER TEST CONDUCTED THROUGH FRACTURED MEDIA  

EPA Science Inventory

The gas-phase partitioning tracer method was used to estimate non-aqueous phase liquid (NAPL), water, and air saturations in the vadose zone at a chlorinated-solvent contaminated field site in Tucson, AZ. The tracer test was conducted in a fractured clay system that is the confin...

288

Confinement effects and deviations from ideality of vapours at the adsorbed phase\\/gas interface  

Microsoft Academic Search

In the present work, confinement effects are evidenced both from the side of the adsorbed phase as well as from the gas phase of the same fluid. A generalization of these confinement effects is proposed by using the corresponding states principle as a classical tool to compare adsorption phenomena. The lowest closure point of hysteresis loop has been chosen because

Stéphane Pariente; Pierre Marie Papineschi; Philippe Trens

2007-01-01

289

THE DEGREE OF PHASE COMPENSATION OF LASER BEAMS USING GAS JETS  

Microsoft Academic Search

When a laser beam propagates in the atmosphere, its phase can be distorted either passively, due to turbulence, or actively, due to thermal blooming. It has been demonstrated that it is possible to partially compensate for these phase errors by physically distorting the transmitting optics. The use of gas jets, with controllable density variation, that are suitably interposed in the

W. H. Christiansen; E. Wasserstrom; A. Hertzberg

1980-01-01

290

Computational Science Technical Note CSTN-132 Visualising Multi-Phase Lattice Gas Fluid Layering Simulations  

E-print Network

insights into the essential behaviours. We describe sim- ulations of multi-phase layering in a lattice gas still reveal good insights into the essential behaviours. We describe simulations of multi Introduction Complex fluids such as multi-phase systems of sand, mud, oil and so forth[1] have attracted

Hawick, Ken

291

Uncertainty and sensitivity analysis of gas-phase chemistry in a CHF3 plasma  

NASA Astrophysics Data System (ADS)

A global uncertainty and sensitivity analysis is performed for a detailed gas-phase reaction set in a CHF3 plasma. The goal of this paper is to ascertain the uncertainties in plasma reactor model results (plasma and radical densities) that originate from the uncertainties in the gas-phase chemistry database. We discuss the rates of reactions and their uncertainties. Comparisons with experimental data show that gas-phase rate uncertainties do not explain the disagreements at higher pressures (>30 mTorr). We also find that electron impact dissociation reactions of dominant neutrals are the largest sources of uncertainties. HF kinetics are also found to be critical in determining radical and feedstock gas densities. Relative ion densities are uncertain due to poor understanding of charge transfer mechanisms.

Bose, Deepak; Rao, M. V. V. S.; Govindan, T. R.; Meyyappan, M.

2003-05-01

292

Influence of gas phase equilibria on the chemical vapor deposition of graphene.  

PubMed

We have investigated the influence of gas phase chemistry on the chemical vapor deposition of graphene in a hot wall reactor. A new extended parameter space for graphene growth was defined through literature review and experimentation at low pressures (?0.001 mbar). The deposited films were characterized by scanning electron microscopy, Raman spectroscopy, and dark field optical microscopy, with the latter showing promise as a rapid and nondestructive characterization technique for graphene films. The equilibrium gas compositions have been calculated across this parameter space. Correlations between the graphene films grown and prevalent species in the equilibrium gas phase revealed that deposition conditions associated with a high acetylene equilibrium concentration lead to good quality graphene deposition, and conditions that stabilize large hydrocarbon molecules in the gas phase result in films with multiple defects. The transition between lobed and hexagonal graphene islands was found to be linked to the concentration of the monatomic hydrogen radical, with low concentrations associated with hexagonal islands. PMID:23484546

Lewis, Amanda M; Derby, Brian; Kinloch, Ian A

2013-04-23

293

Lipase hydration state in the gas phase: Sorption isotherm measurements and inverse gas chromatography.  

E-print Network

chromatography. Zsuzsanna Marton1 , Ludovic Chaput1 , Guillaume Pierre1 and Marianne Graber1 1 Université de la Rochelle, Cedex 01, France. Keywords: Water, Lipase, Adsorption, Inverse Gas Chromatography, Solid@univ-lr.fr Fax : +33 5 46 45 82 65 Abbreviations: IGC, Inverse Gas Chromatography aW, water thermodynamic

Paris-Sud XI, Université de

294

Quantizing field-induced magnetic phase in a three-dimensional electron gas  

NASA Astrophysics Data System (ADS)

Theory of magnetic-induction bifurcation in the Condon domain phase of a three-dimensional (3D) electron gas under high-magnetic field is presented. The results-the diamagnetic phase transition temperature and the induction bifurcation values-are in good agreement with nuclear magnetic resonance data in silver. The temperature dependence of the order parameter of the diamagnetic phase transition-the magnetization in each Condon domain-is obtained by a comparison of the theory with the experiment. The mean-field approach has been shown to lead to the universal behavior of an electron gas of 2D and 3D dimensionality.

Gordon, A.; Itskovsky, M. A.; Wyder, P.

1999-04-01

295

Analysis of volatile phase transport in soils using natural radon gas as a tracer  

SciTech Connect

We have conducted a field study of soil gas transport processes using radon gas as a naturally occurring tracer. The .experiment monitored soil gas radon activity, soil moisture, and soil temperature at three depths in the shallow soil column; barometric pressure, rainfall and wind speed were monitored at the soil surface. Linear and multiple regression analysis of the data sets has shown that the gas phase radon activities under natural environmental conditions are influenced by soil moisture content, barometric pressure variations, soil temperature and soil structure. The effect of wind speed on subsurface radon activities under our field conditions has not been demonstrated.

Chen, C.; Thomas, D.M.

1992-12-31

296

Dynamic damage nucleation and evolution in multiphase materials  

NASA Astrophysics Data System (ADS)

For ductile metals, dynamic fracture occurs through void nucleation, growth, and coalescence. Previous experimental works in high purity metals have shown that microstructural features such as grain boundaries, inclusions, vacancies, and heterogeneities can act as initial void nucleation sites. However, for materials of engineering significance, those with, second phase particles it is less clear what the role of a soft second phase will be on damage nucleation and evolution. To approach this problem in a systematic manner, two materials have been investigated: high purity copper and copper with 1% lead. These materials have been shock loaded at ˜1.5 GPa and soft recovered. In-situ free surface velocity information and post mortem metallography reveals the presence of a high number of small voids in CuPb in comparison to a lower number of large voids in Cu. This suggests that damage evolution is nucleation dominated in the CuPb and growth dominated in the pure Cu.

Fensin, S. J.; Escobedo, J. P.; Gray, G. T.; Patterson, B. M.; Trujillo, C. P.; Cerreta, E. K.

2014-05-01

297

Characteristic Analysis of Gas\\/Liquid Two-Phase Flow Regimes Based on Wavelet Packet Entropy  

Microsoft Academic Search

The identification of flow regime is the basis for measuring flow parameters in two-phase flow accurately. Because of the complexity of phase interaction in gas-liquid two-phase flow, it is difficult to discern its flow regime objectively. In this paper, the 208 measured data from electrical resistance tomography (ERT) are arranged into series based on section to investigate the dynamic characteristics

Chun Fu; Feng Dong

2010-01-01

298

Studies of two-phase gas-liquid flow in microgravity  

Microsoft Academic Search

Two-phase gas-liquid flows are expected to occur in many future space operations. Due to a lack of buoyancy in the microgravity environment, two-phase flows are known to behave differently than those in earth gravity. Despite these concerns, little research has been conducted on microgravity two-phase flow and the current understanding is poor. This dissertation describes an experimental and modeling study

William Scott Bousman

1995-01-01

299

A gas-phase source term for Yucca Mountain  

Microsoft Academic Search

We previously presented analyses of gas flow into and out of a partly failed nuclear waste container for various assumed hole sizes and failure times. We also estimated the release rate of ¹⁴C by advection and counter-diffusion from the failed container. Here we present an estimate of ¹⁴C release rate and cumulative release for hole sizes of one to 300-μm

E. D. Zwahlen; W. W. L. Lee; T. H. Pigford; P. L. Chambre

1990-01-01

300

Phase I: the pipeline gas demonstration plant. Site selection report  

Microsoft Academic Search

Contract No. EF-77-C-01-2542 between Continental Oil Company and the United States Department of Energy (DOE) requires Continental Oil to analyze, design, construct, test, evaluate, and operate a Demonstration Plant capable of converting high-sulfur bituminous caking coal to a high-Btu pipeline quality gas. One of the assignments under the contract is to select the site for constructing the Demonstration Plant. A

Leaman; G. J. Jr

1977-01-01

301

Deposition nucleation viewed as homogeneous or immersion freezing in pores and cavities  

NASA Astrophysics Data System (ADS)

Heterogeneous ice nucleation is an important mechanism for the glaciation of mixed phase clouds and may also be relevant for cloud formation and dehydration at the cirrus cloud level. It is thought to proceed through different mechanisms, namely contact, condensation, immersion and deposition nucleation. Supposedly, deposition nucleation is the only pathway which does not involve liquid water but occurs by direct water vapor deposition on a surface. This study challenges this classical view by putting forward the hypothesis that what is called deposition nucleation is in fact homogeneous or immersion nucleation occurring in pores and cavities that may form between aggregated primary particles and fill with water at relative humidity RHw < 100% because of the inverse Kelvin effect. Evidence for this hypothesis of pore condensation and freezing (PCF) originates from a number of only loosely connected scientific areas. The prime example for PCF is ice nucleation in clay minerals and mineral dusts, for which the data base is best. Studies on freezing in confinement carried out on mesoporous silica materials such as SBA-15, SBA-16, MCM-41, zeolites and KIT have shown that homogeneous ice nucleation occurs abruptly at T=230-235 K in pores with diameters (D) of 3.5-4 nm or larger but only gradually at T=210-230 K in pores with D=2.5-3.5 nm. Melting temperatures in pores are depressed by an amount that can be described by the Gibbs-Thomson equation. Water adsorption isotherms of MCM-41 show that pores with D=3.5-4 nm fill with water at RHw = 56-60% in accordance with an inverse Kelvin effect. Water in such pores should freeze homogeneously for T < 235 K even before relative humidity with respect to ice (RHi) reaches ice saturation. Ice crystal growth by water vapor deposition from the gas phase is therefore expected to set in as soon as RHw > 100%. Pores with D > 7.5 nm fill with water at RHi > 100% for T < 235 K and are likely to freeze homogeneously as soon as they are filled with water. Water in pores can freeze in immersion mode at T > 235 K if the pore walls contain an active site. Pore analysis of clay minerals shows that kaolinites exhibit pore structures with pore diameters of 20-50 nm. The mesoporosity of illites and montmorillonites is characterized by pores with T = 2-5 nm. The number and size of pores is distinctly increased in acid treated montmorillonites like K10. Many clay minerals and mineral dusts show a strong increase in ice nucleation efficiency when temperature is decreased below 235 K. Such an increase is difficult to explain when ice nucleation is supposed to occur by a deposition mechanism, but evident when assuming freezing in pores, because for homogeneous ice nucleation only small pore volumes are needed, while heterogeneous ice nucleation requires larger pore structures to contain at least one active site for immersion nucleation. Together, these pieces of evidence strongly suggest that ice nucleation within pores should be the prevailing freezing mechanism of clay minerals for RHw below water saturation. Extending the analysis to other types of ice nuclei shows that freezing in pores and cracks is probably the prevailing ice nucleation mechanism for glassy and volcanic ash aerosols at RHw below water saturation. Freezing of water in carbon nanotubes might be of significance for ice nucleation by soot aerosols. No case could be identified that gives clear evidence of ice nucleation by water vapor deposition on a solid surface. Inspection of ice nuclei with a close lattice match to ice, such as silver iodide or SnomaxTM, show that for high ice nucleation efficiency below water saturation the presence of impurities or cracks on the surface may be essential. Soluble impurities promote the formation of a liquid phase below water saturation in patches on the surface or as a complete surface layer that offers an environment for immersion freezing. If porous aerosol particles come in contact with semivolatile vapors, these will condense preferentially in pores before a coating on

Marcolli, C.

2013-06-01

302

Liquid to solid nucleation via onion structure droplets  

NASA Astrophysics Data System (ADS)

We study homogeneous nucleation from a deeply quenched metastable liquid to a spatially modulated phase. We find, for a general class of density functional theories, that the universally favored nucleating droplet in dimensions d ? 3 is spherically symmetric with radial modulations resembling the layers of an onion. The existence of this droplet has important implications for systems with effective long-range interactions, and potentially applies to polymers, plasmas, and metals.

Barros, Kipton; Klein, W.

2013-11-01

303

Surface Nanobubbles Nucleate Microdroplets  

NASA Astrophysics Data System (ADS)

When a hydrophobic solid is in contact with water, surface nanobubbles often form at the interface. They have a lifetime many orders of magnitude longer than expected. Here, we show that they even withstand a temperature increase to temperatures close to the boiling point of bulk water; i.e., they do not nucleate larger bubbles ("superstability"). On the contrary, when the vapor-liquid contact line passes a nanobubble, a liquid film remains around it, which, after pinch-off, results in a microdroplet in which the nanobubbles continue to exist. Finally, the microdroplet evaporates and the nanobubble consequently bursts. Our results support that pinning plays a crucial role for nanobubble stability.

Zhang, Xuehua; Lhuissier, Henri; Sun, Chao; Lohse, Detlef

2014-04-01

304

Nova Dust Nucleation: Kinetics and Photodissociation  

E-print Network

Dust is observed to form in nova ejecta. The grain temperature is determined by the diluted nova radiation field rather than the gas kinetic temperature, making classical nucleation theory inapplicable. We used kinetic equations to calculate the growth of carbon nuclei in these ejecta. For expected values of the parameters too many clusters grew, despite the small sticking probability of atoms to small clusters, and the clusters only reached radii of about 100\\AA\\ when the carbon vapor was depleted. We then included the effects of cluster photodissociation by ultraviolet radiation from the nova. This suppresses nucleation, but too well, and no grains form at all. Finally we suggest that a few growing carbon nuclei may be protected from photodissociation by a sacrificial surface layer of hydrogen.

D. J. Johnson; M. W. Friedlander; J. I. Katz

1992-04-30

305

Nova dust nucleation - Kinetics and photodissociation  

NASA Technical Reports Server (NTRS)

Dust is observed to form in nova ejecta. The grain temperature is determined by the diluted nova radiation field rather than the gas kinetic temperature, making classical nucleation theory inapplicable. We used kinetic equations to calculate the growth of carbon nuclei in these ejecta. For expected values of the parameters too many clusters grew, despite the small sticking probability of atoms to small clusters, and the clusters only reached radii of about 100 A when the carbon vapor was depleted. We then included the effects of cluster photodissociation by ultraviolet radiation from the nova. This suppresses nucleation, but too well, and no grains form at all. Finally we suggest that a few growing carbon nuclei may be protected from photodissociation by a sacrificial surface layer of hydrogen.

Johnson, D. J.; Friedlander, M. W.; Katz, J. I.

1993-01-01

306

Gas chromatography on wall-coated open-tubular columns with ionic liquid stationary phases.  

PubMed

Ionic liquids have moved from novel to practical stationary phases for gas chromatography with an increasing portfolio of applications. Ionic liquids complement conventional stationary phases because of a combination of thermophysical and solvation properties that only exist for ionic solvents. Their high thermal stability and low vapor pressure makes them suitable as polar stationary phases for separations requiring high temperatures. Ionic liquids are good solvents and can be used to expand the chemical space for separations. They are the only stationary phases with significant hydrogen-bond acidity in common use; they extend the hydrogen-bond basicity of conventional stationary phases; they are as dipolar/polarizable as the most polar conventional stationary phases; and some ionic liquids are significantly less cohesive than conventional polar stationary phases. Problems in column coating techniques and related low column performance, column activity, and stationary phase reactivity require further exploration as the reasons for these features are poorly understood at present. PMID:24690306

Poole, Colin F; Lenca, Nicole

2014-08-29

307

Geometry as a catalyst: how vapor cavities nucleate from defects.  

PubMed

The onset of cavitation is strongly enhanced by the presence of rough surfaces or impurities in the liquid. Despite decades of research, the way the geometry of these defects promote the nucleation of bubbles and its effect on the kinetics of the process remains largely unclear. We present here a comprehensive explanation of the catalytic action that roughness elements exert on the nucleation process for both pure vapor cavities and gas ones. This approach highlights that nucleation may follow nontrivial paths connected with a sharp decrease of the free energy barriers as compared to flat surfaces. Furthermore, we demonstrate the existence of intermediate metastable states that break the nucleation process in multiple steps; these states correspond to what is commonly known as cavitation nuclei. A single dimensionless parameter, the nucleation number, is found to control this rich phenomenology. The devised theory allows one to quantify the effect of the geometry and hydrophobicity of surface asperities on nucleation. Within the same framework, it is possible to treat both vapor cavitation, which is relevant, e.g., for organic liquids, and gas-promoted cavitation, which is commonly encountered in water. The theory is shown to be valid from the nano- to the macroscale. PMID:24205896

Giacomello, Alberto; Chinappi, Mauro; Meloni, Simone; Casciola, Carlo Massimo

2013-12-01

308

Modelling non-equilibrium secondary organic aerosol formation and evaporation with the aerosol dynamics, gas- and particle-phase chemistry kinetic multi-layer model ADCHAM  

NASA Astrophysics Data System (ADS)

We have developed the novel Aerosol Dynamics, gas- and particle-phase chemistry model for laboratory CHAMber studies (ADCHAM). The model combines the detailed gas phase Master Chemical Mechanism version 3.2, an aerosol dynamics and particle phase chemistry module (which considers acid catalysed oligomerization, heterogeneous oxidation reactions in the particle phase and non-ideal interactions between organic compounds, water and inorganic ions) and a kinetic multilayer module for diffusion limited transport of compounds between the gas phase, particle surface and particle bulk phase. In this article we describe and use ADCHAM to study: (1) the mass transfer limited uptake of ammonia (NH3) and formation of organic salts between ammonium (NH4+) and carboxylic acids (RCOOH), (2) the slow and almost particle size independent evaporation of ?-pinene secondary organic aerosol (SOA) particles, and (3) the influence of chamber wall effects on the observed SOA formation in smog chambers. ADCHAM is able to capture the observed ?-pinene SOA mass increase in the presence of NH3(g). Organic salts of ammonium and carboxylic acids predominantly form during the early stage of SOA formation. These salts contribute substantially to the initial growth of the homogeneously nucleated particles. The model simulations of evaporating ?-pinene SOA particles support the recent experimental findings that these particles have a semi-solid tar like amorphous phase state. ADCHAM is able to reproduce the main features of the observed slow evaporation rates if low-volatility and viscous oligomerized SOA material accumulates in the particle surface layer upon evaporation. The evaporation rate is mainly governed by the reversible decomposition of oligomers back to monomers. Finally, we demonstrate that the mass transfer limited uptake of condensable organic compounds onto wall deposited particles or directly onto the Teflon chamber walls of smog chambers can have profound influence on the observed SOA formation. During the early stage of the SOA formation the wall deposited particles and walls themselves serve as a SOA sink from the air to the walls. However, at the end of smog chamber experiments the semi-volatile SOA material may start to evaporate from the chamber walls. With these three model applications, we demonstrate that several poorly quantified processes, i.e. mass transport limitations within the particle phase, oligomerization, heterogeneous oxidation, organic salt formation, and chamber wall effects can have substantial influence on the SOA formation, lifetime, chemical and physical particle properties, and their evolution. In order to constrain the uncertainties related to these processes, future experiments are needed where as many of the influential variables as possible are varied. ADCHAM can be a valuable model tool in the design and analysis of such experiments.

Roldin, P.; Eriksson, A. C.; Nordin, E. Z.; Hermansson, E.; Mogensen, D.; Rusanen, A.; Boy, M.; Swietlicki, E.; Svenningsson, B.; Zelenyuk, A.; Pagels, J.

2014-01-01

309

Characteristics of three-phase internal loop airlift bioreactors with complete gas recirculation for non-Newtonian fluids  

Microsoft Academic Search

Hydrodynamic and gas–liquid mass transfer characteristics, such as liquid velocity, gas holdup, solid holdup and gas–liquid volumetric mass transfer coefficient, in the riser and downcomer of the gas–liquid-solid three-phase internal loop airlift bioreactors with complete gas recirculation for non-Newtonian fluids, were investigated. A mathematical model for the description of flow behavior and gas–iquid mass transfer of these bioreactors was developed.

Jianping Wen; Xiaoqiang Jia; Xianrui Cheng; Peng Yang

2005-01-01

310

Substrate orientation effects on the nucleation and growth of the M{sub n+1}AX{sub n} phase Ti{sub 2}AlC  

SciTech Connect

The M{sub n+1}AX{sub n} (MAX) phases are ternary compounds comprising alternating layers of a transition metal carbide or nitride and a third ''A-group'' element. The effect of substrate orientation on the growth of Ti{sub 2}AlC MAX phase films was investigated by studying pulsed cathodic arc deposited samples grown on sapphire cut along the (0001), (1010), and (1102) crystallographic planes. Characterization of these samples was by x-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. On the (1010) substrate, tilted (1018) growth of Ti{sub 2}AlC was found, such that the TiC octahedra of the MAX phase structure have the same orientation as a spontaneously formed epitaxial TiC sublayer, preserving the typical TiC-Ti{sub 2}AlC epitaxial relationship and confirming the importance of this relationship in determining MAX phase film orientation. An additional component of Ti{sub 2}AlC with tilted fiber texture was observed in this sample; tilted fiber texture, or axiotaxy, has not previously been seen in MAX phase films.

Tucker, Mark D.; Guenette, Mathew C.; Bilek, Marcela M. M.; McKenzie, David R. [School of Physics, University of Sydney, New South Wales 2006 (Australia); Persson, Per O. A.; Rosen, Johanna [School of Physics, University of Sydney, New South Wales 2006 (Australia); Thin Film Physics, Linkoepings Universitet, 58183 Linkoeping (Sweden)

2011-01-01

311

Efficient and directed peptide bond formation in the gas phase via ion/ion reactions  

PubMed Central

Amide linkages are among the most important chemical bonds in living systems, constituting the connections between amino acids in peptides and proteins. We demonstrate the controlled formation of amide bonds between amino acids or peptides in the gas phase using ion/ion reactions in a mass spectrometer. Individual amino acids or peptides can be prepared as reagents by (i) incorporating gas phase–labile protecting groups to silence otherwise reactive functional groups, such as the N terminus; (ii) converting the carboxyl groups to the active ester of N-hydroxysuccinimide; and (iii) incorporating a charge site. Protonation renders basic sites (nucleophiles) unreactive toward the N-hydroxysuccinimide ester reagents, resulting in sites with the greatest gas phase basicities being, in large part, unreactive. The N-terminal amines of most naturally occurring amino acids have lower gas phase basicities than the side chains of the basic amino acids (i.e., those of histidine, lysine, or arginine). Therefore, reagents may be directed to the N terminus of an existing “anchor” peptide to form an amide bond by protonating the anchor peptide’s basic residues, while leaving the N-terminal amine unprotonated and therefore reactive. Reaction efficiencies of greater than 30% have been observed. We propose this method as a step toward the controlled synthesis of peptides in the gas phase. PMID:24474750

McGee, William M.; McLuckey, Scott A.

2014-01-01

312

Dynamical phases in quenched spin–orbit-coupled degenerate Fermi gas  

NASA Astrophysics Data System (ADS)

The spin–orbit-coupled degenerate Fermi gas provides a new platform for realizing topological superfluids and related topological excitations. However, previous studies have been mainly focused on the topological properties of the stationary ground state. Here, we investigate the quench dynamics of a spin–orbit-coupled two-dimensional Fermi gas in which the Zeeman field serves as the major quench parameter. Three post-quench dynamical phases are identified according to the asymptotic behaviour of the order parameter. In the undamped phase, a persistent oscillation of the order parameter may support a topological Floquet state with multiple edge states. In the damped phase, the magnitude of the order parameter approaches a constant via a power-law decay, which may support a dynamical topological phase with one edge state at the boundary. In the overdamped phase, the order parameter decays to zero exponentially although the condensate fraction remains finite. These predictions can be observed in the strong-coupling regime.

Dong, Ying; Dong, Lin; Gong, Ming; Pu, Han

2015-01-01

313

Strategies for the Gas Phase Modification of Cationized Arginine via Ion/ion Reactions  

PubMed Central

The gas phase acetylation of cationized arginine residues is demonstrated here using ion/ion reactions with sulfosuccinimidyl acetate (sulfo-NHS acetate) anions. Previous reports have demonstrated the gas phase modification of uncharged primary amine (the N-terminus and ?-amino side chain of lysine) and uncharged guanidine (the arginine side chain) functionalities via sulfo-NHS ester chemistry. Herein, charge-saturated arginine-containing peptides that contain sodium ions as the charge carriers, such as [ac-ARAAARA+2Na]2+, are shown to exhibit strong reactivity towards sulfo-NHS acetate whereas the protonated peptide analogues exhibit no such reactivity. This difference in reactivity is attributed to the lower sodium ion (as compared to proton) affinity of the arginine, which results in increased nucleophilicity of the cationized arginine guanidinium functionality. This increased nucleophilicity improves the arginine residue's reactivity towards sulfo-NHS esters and enhances the gas phase covalent modification pathway. No such dramatic increase in reactivity towards sulfo-NHS acetate has been observed upon sodium cationization of lysine amino acid residues, indicating that this behavior appears to be unique to arginine. The sodium cationization process is demonstrated in the condensed phase by simply spiking sodium chloride into the peptide sample solution and in the gas phase by a peptide-sodium cation exchange process with a sulfo-NHS acetate sodium-bound dimer cluster reagent. This methodology demonstrates several ways by which arginine can be covalently modified in the gas phase even when it is charged. Collisional activation of an acetylated arginine product can result in deguanidination of the residue, generating an ornithine. This gas phase ornithination exhibits similar site-specific fragmentation behavior to that observed with peptides ornithinated in solution and may represent a useful approach for inducing selective peptide cleavages. PMID:24273437

Prentice, Boone M.; McGee, William M.; Stutzman, John R.; McLuckey, Scott A.

2013-01-01

314

Nucleation of Nuclear Bodies  

PubMed Central

The nucleus is a complex organelle containing numerous highly dynamic, structurally stable domains and bodies, harboring functions that have only begun to be defined. However, the molecular mechanisms for their formation are still poorly understood. Recently it has been shown that a nuclear body can form de novo by self-organization. But little is known regarding what triggers the formation of a nuclear body and how subsequent assembly steps are orchestrated. Nuclear bodies are frequently associated with specific active gene loci that directly contribute to their formation. Both coding and noncoding RNAs can initiate the assembly of nuclear bodies with which they are physiologically associated. Thus, the formation of nuclear bodies occurs via recruitment and consequent accumulation of resident proteins in the nuclear bodies by nucleating RNA acting as a seeder. In this chapter I describe how to set up an experimental cell system to probe de novo biogenesis of a nuclear body by nucleating RNA and nuclear body components tethered on chromatin. PMID:23980018

Dundr, Miroslav

2014-01-01

315

Factors controlling the ice nucleating abilities of ?-pinene SOA particles  

NASA Astrophysics Data System (ADS)

The ice nucleation abilities of fresh, water-soluble, internally mixed, and photochemically oxidized ?-pinene secondary organic aerosol (SOA) particles were investigated at cirrus cloud temperatures in a continuous flow diffusion chamber. SOA sampled from a flow tube (SOA-fresh-FT) mimicked freshly generated particles, while the water-soluble organic compound fraction from a FT and smog chamber (SOA-WSOC-FT, SOA-WSOC-SC) mimicked cloud-processed particles. SOA-fresh-FT, SOA-WSOC-FT, and SOA-WSOC-SC particles were not highly active at nucleating ice between 233 K and 213 K, with activation onsets (i.e., 0.1% of particles forming ice) at or slightly above the theoretical homogeneous freezing line. A significant increase in the O/C of SOA-WSOC-SC via aqueous phase OH oxidation did not modify the ice nucleation abilities, indicating that the detailed composition of the particles is not of paramount importance to their ice nucleating abilities. Instead, precooling the SOA-WSOC-FT and SOA-WSOC-SC particles to 233 K dropped their ice nucleation onsets by up to 20% relative humidity with respect to ice, with lower temperatures likely driving the particles to be more viscous and solid-like. However, it is possible that preactivation contributed to the reduction of the ice nucleation onsets. Particles composed of both SOA-WSOC and ammonium sulfate (AS) were significantly less active in the deposition nucleation mode than pure, solid AS particles.

Ladino, L. A.; Zhou, S.; Yakobi-Hancock, J. D.; Aljawhary, D.; Abbatt, J. P. D.

2014-07-01

316

OMVPE growth and gas-phase reactions of AlGaN for UV emitters  

SciTech Connect

Gas-phase parasitic reactions among TMG, TMA, and NH3, are investigated by monitoring of the growth rate/incorporation efficiency of GaN and AlN using an in-situ optical reflectometer. It is suggested that gas phase adduct (TMA: NH{sub 3}) reactions not only reduce the incorporation efficiency of TMA but also affect the incorporation behavior of TMGa. The observed phenomena can be explained by either a synergistic gas-phase scavenging effect or a surface site-blocking effect. Relatively low reactor pressures (30--50 Torr) are employed to grow an AlGaN/GaN QW p-n diode structure. The UV emission at 354 nm (FWHM {approximately} 6 nm) represents the first report of LED operation from an indium-free GaN QW diode.

Han, J.; Figiel, J.J.; Crawford, M.H.; Banas, M.A.; Bartram, M.E.; Biefeld, R.M. [Sandia National Labs., Albuquerque, NM (United States); Song, Y.K.; Nurmikko, A.V. [Brown Univ., Providence, RI (United States). Div. of Engineering

1998-06-01

317

Do all the protic ionic liquids exist as molecular aggregates in the gas phase?  

PubMed

According to an EI-MS study of 1,1,3,3-tetramethylguanidium-based protic ionic liquids (PILs), it has been concluded that not all PILs exist as molecular aggregates in the gas phase. The detection of both ions of m/z 115.0 and m/z 116.0 for the 1,1,3,3-tetramethylguanidinium trifluoromethylsulfonate (TMGS) protic ionic liquid indicates that both the molecular and ionic aggregates co-exist in the gas phase, which is to say that the TMGS may also evaporate via the ionic aggregates just like aprotic ionic liquids. Furthermore, investigation on triethylamine-based and 1-methylimidazole-based PILs confirmed that the gas phase structure of PILs depends on both the acidity and basicity of the corresponding acid and base. PMID:21897972

Zhu, Xiao; Wang, Yong; Li, Haoran

2011-10-21

318

Gas-phase ambident reactivity of imidate anions (-NR1(CO)R2)  

NASA Astrophysics Data System (ADS)

It is shown by use of the method of Fourier transform ion cyclotron resonance mass spectrometry that imidate anions, generated by deprotonation of formamide, acetamide, N-methylformamide and trifluoroacetamide, exhibit an ambident chemical behavior in their gas-phase reactions with unsaturated perfluorocarbon compounds. This ambident behavior implies a competition between addition via the nitrogen and oxygen nucleophilic centers and appears to parallel the previously-studied ambident behavior of enolate anions in the gas phase. Rationalization of the selectivity of the studied imidate anion reactions has been discussed in terms of electrostatic and specific orbital interactions in the reaction complex. Likewise, thio-imidate anions generated by deprotonation of thioacetamide show an ambident chemical behavior which allows a fair competition between addition via the nitrogen and sulfur nucleophilic centers in the gas-phase reactions with unsaturated perfluorocarbon compounds.

Freriks, Ivo L.; de Koning, Leo J.; Nibbering, Nico M. M.

1992-09-01

319

Device for two-dimensional gas-phase separation and characterization of ion mixtures  

DOEpatents

The present invention relates to a device for separation and characterization of gas-phase ions. The device incorporates an ion source, a field asymmetric waveform ion mobility spectrometry (FAIMS) analyzer, an ion mobility spectrometry (IMS) drift tube, and an ion detector. In one aspect of the invention, FAIMS operating voltages are electrically floated on top of the IMS drift voltage. In the other aspect, the FAIMS/IMS interface is implemented employing an electrodynamic ion funnel, including in particular an hourglass ion funnel. The present invention improves the efficiency (peak capacity) and sensitivity of gas-phase separations; the online FAIMS/IMS coupling creates a fundamentally novel two-dimensional gas-phase separation technology with high peak capacity, specificity, and exceptional throughput.

Tang, Keqi (Richland, WA); Shvartsburg, Alexandre A. (Richland, WA); Smith, Richard D. (Richland, WA)

2006-12-12

320

Effect of Inlet Geometry on Adiabatic Gas-Liquid Two-Phase Flow in a Microchannel  

Microsoft Academic Search

An optical measurement system and video camera were used to investigate gas-liquid two-phase flow characteristics in a circular microchannel of 100 ?m diameter. By cross-correlating the signals from two pairs of optical fibers and infrared photodiodes, void fraction and the lengths and velocities of gas slugs and liquid slugs were measured. The data were obtained using a T-junction with the

Hideo Ide; Ryuji Kimura; Masahiro Kawaji

2008-01-01

321

Measurements of liquid-phase turbulence in gas-liquid two-phase flows using particle image velocimetry  

NASA Astrophysics Data System (ADS)

Liquid-phase turbulence measurements were performed in an air-water two-phase flow loop with a circular test section of 50 mm inner diameter using a particle image velocimetry (PIV) system. An optical phase separation method--planar laser-induced fluorescence (PLIF) technique—which uses fluorescent particles and an optical filtration technique, was employed to separate the signals of the fluorescent seeding particles from those due to bubbles and other noises. An image pre-processing scheme was applied to the raw PIV images to remove the noise residuals that are not removed by the PLIF technique. In addition, four-sensor conductivity probes were adopted to measure the radial distribution of the void fraction. Two benchmark tests were performed: the first was a comparison of the PIV measurement results with those of similar flow conditions using thermal anemometry from previous studies; the second quantitatively compared the superficial liquid velocities calculated from the local liquid velocity and void fraction measurements with the global liquid flow rate measurements. The differences of the superficial liquid velocity obtained from the two measurements were bounded within ±7% for single-phase flows and two-phase bubbly flows with the area-average void fraction up to 18%. Furthermore, a preliminary uncertainty analysis was conducted to investigate the accuracy of the two-phase PIV measurements. The systematic uncertainties due to the circular pipe curvature effects, bubble surface reflection effects and other potential uncertainty sources of the PIV measurements were discussed. The purpose of this work is to facilitate the development of a measurement technique (PIV-PLIF) combined with image pre-processing for the liquid-phase turbulence in gas-liquid two-phase flows of relatively high void fractions. The high-resolution data set can be used to more thoroughly understand two-phase flow behavior, develop liquid-phase turbulence models, and assess high-fidelity codes for multi-phase flows.

Zhou, Xinquan; Doup, Benjamin; Sun, Xiaodong

2013-12-01

322

Nucleation and growth of tin whiskers  

NASA Astrophysics Data System (ADS)

Pure tin film of one micron thick was evaporated onto a silicon substrate with chromium and nickel underlayers. The tinned silicon disk was bent by applying a dead load at the center and supported below around the edge to apply biaxial compressive stresses to the tin layer. After 180 C vacuum annealing for 1,2,4,6, and 8 weeks, tin whiskers/hillocks grew. A quantitative method revealed that the overall growth rate decreased with time with a tendency for saturation. A review of the literature showed in general, tin whisker growth has a nucleation period, a growth period and a period of saturation, very similar to recrystallization or phase transformation. In fact we found our data fit Avrami equation very well. This equation shows that the nucleation period was the first week.

Cheng, Jing; Vianco, Paul T.; Zhang, Bei; Li, James C. M.

2011-06-01

323

Accelerated decomposition of gas phase metal organic molecules determined by radical reactions  

NASA Astrophysics Data System (ADS)

The reactivity of gas phase radicals generated during the MOCVD of GaAs, GaN, ZnS, ZnSe, and CdTe was studied using density functional theory. Calculations were performed with B3LYP functionals and different basis sets. It was found that the production of CH 3 through surface reactions is an intrinsic part of the growth process when using Ga(CH 3) 3, Zn(CH 3) 2, or Cd(CH 3) 2 as gas phase precursors. After being generated, CH 3 can react with the organometallic molecules or with H 2, if it is used as carrier gas, to give CH 4 and H. Atomic hydrogen is much more reactive than CH 3 and can easily decompose Ga(CH 3) 3 and Cd(CH 3) 2 to GaCH 3 and CdCH 3, which leads to an increase of the film growth rate. When reacting with H 2Se, H can start a radical chain mechanism that can eventually determine the formation of large ZnSe gas phase adducts. Finally, it was found that H can react with NH 3 to give NH 2, which can then react with Ga(CH 3) 3 to give Ga(CH 3) 2NH 2 and successively form GaN gas phase adducts.

Cavallotti, Carlo; Moscatelli, Davide; Masi, Maurizio; Carrà, Sergio

2004-05-01

324

Plasma-produced phase-pure cuprous oxide nanowires for methane gas sensing  

SciTech Connect

Phase-selective synthesis of copper oxide nanowires is warranted by several applications, yet it remains challenging because of the narrow windows of the suitable temperature and precursor gas composition in thermal processes. Here, we report on the room-temperature synthesis of small-diameter, large-area, uniform, and phase-pure Cu{sub 2}O nanowires by exposing copper films to a custom-designed low-pressure, thermally non-equilibrium, high-density (typically, the electron number density is in the range of 10{sup 11}–10{sup 13}?cm{sup ?3}) inductively coupled plasmas. The mechanism of the plasma-enabled phase selectivity is proposed. The gas sensors based on the synthesized Cu{sub 2}O nanowires feature fast response and recovery for the low-temperature (?140?°C) detection of methane gas in comparison with polycrystalline Cu{sub 2}O thin film-based gas sensors. Specifically, at a methane concentration of 4%, the response and the recovery times of the Cu{sub 2}O nanowire-based gas sensors are 125 and 147?s, respectively. The Cu{sub 2}O nanowire-based gas sensors have a potential for applications in the environmental monitoring, chemical industry, mining industry, and several other emerging areas.

Cheng, Qijin, E-mail: ijin.cheng@xmu.edu.cn; Zhang, Fengyan [School of Energy Research, Xiamen University, Xiamen City, Fujian Province 361005 (China); Yan, Wei [School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales 2052 (Australia); Plasma Nanoscience Laboratories, CSIRO Materials Science and Engineering, Lindfield, New South Wales 2070 (Australia); Randeniya, Lakshman [Plasma Nanoscience Laboratories, CSIRO Materials Science and Engineering, Lindfield, New South Wales 2070 (Australia); Ostrikov, Kostya [Plasma Nanoscience Laboratories, CSIRO Materials Science and Engineering, Lindfield, New South Wales 2070 (Australia); Plasma Nanoscience, School of Physics, The University of Sydney, Sydney, New South Wales 2006 (Australia)

2014-03-28

325

Atmospheric chemistry of gas-phase polycyclic aromatic hydrocarbons: formation of atmospheric mutagens.  

PubMed Central

The atmospheric chemistry of the 2- to 4-ring polycyclic aromatic hydrocarbons (PAH), which exist mainly in the gas phase in the atmosphere, is discussed. The dominant loss process for the gas-phase PAH is by reaction with the hydroxyl radical, resulting in calculated lifetimes in the atmosphere of generally less than one day. The hydroxyl (OH) radical-initiated reactions and nitrate (NO3) radical-initiated reactions often lead to the formation of mutagenic nitro-PAH and other nitropolycyclic aromatic compounds, including nitrodibenzopyranones. These atmospheric reactions have a significant effect on ambient mutagenic activity, indicating that health risk assessments of combustion emissions should include atmospheric transformation products. PMID:7821285

Atkinson, R; Arey, J

1994-01-01

326

Phenomenological model of phase transformations of gas hydrates in porous media: Visco-plastic consolidated skeleton  

NASA Astrophysics Data System (ADS)

We develop a phenomenological model to describe the behavior of natural porous media saturated with phases that can experience phase transformations which result in changes of the strength, rheology, and transport properties of the medium. A porous medium saturated with gas hydrates cementing the grains of a mineral skeleton is an example of such behavior. On a decrease in pressure or increase in temperature, hydrates in such a medium dissociate into gas and water. The resulting fluid acts as a lubricant between the skeleton grains: the elastic response is changed by the viscous response, and the processes of consolidation and multiphase filtration in the deforming skeleton are initiated.

Izvekov, O. Ya.; Konyukhov, A. V.

2013-11-01

327

Study of Hind Limb Tissue Gas Phase Formation in Response to Suspended Adynamia and Hypokinesia  

NASA Technical Reports Server (NTRS)

The purpose of this study was to investigate the hypothesis that reduced joint/muscle activity (hypo kinesia) as well as reduced or null loading of limbs (adynamia) in gravity would result in reduced decompression-induced gas phase and symptoms of decompression sickness (DCS). Finding a correlation between the two phenomena would correspond to the proposed reduction in tissue gas phase formation in astronauts undergoing decompression during extravehicular activity (EVA) in microgravity. The observation may further explain the reported low incidence of DCS in space.

Butler, Bruce D.

1996-01-01

328

Nonthermal Initiation of Nucleation and Chondrule Texture Development  

NASA Astrophysics Data System (ADS)

The textures of chondrules are almost universally ascribed to the influence of heating and cooling histories of the precursor materials. Many chondrule textures are viewed as constraining the cooling history of precursor droplets of silicate liquid that were initially heated to near liquidus temperatures. The standard thermal model uses a superliquidus silicate droplet that was significantly undercooled to induce nucleation and then cooled, possibly nonlinearly, down a thermal gradient to induce crystal growth in the chondrule. Alternately, nuclei may occur as relicts in the droplet or may be introduced as dust on the surface of the droplet. The means by which the nucleation barrier (the essential first step in the crystal growth history of a chondrule) is overcome has fundamental influence on the subsequent development and type of texture - the development of dendritic and porprhyritic textures reflect quite different nucleation histories. We explore an alternate method of 'jumping' this barrier. Undercooling or, more generally, supersaturation of the liquidus solid, can be induced either by cooling an isochemical system from superliquidus temperatures or by isothermally making the bulk composition of the system more refractory. Removal of some FeO from a liquid of typical chondrule bulk composition increases the liquidus temperature and supersaturates the liquid with the most refractory solid, olivine. FeO is removed easily by reduction to metal. Most chondrules are more magnesian than the solar system composition and indeed most are more magnesian than the host meteorite in which they occur. Clearly the source materials of chondrules have lost Fe relative to either bulk solar system or chondritic precursors. If reduction was involved in chondrule formation then Fe-loss would induce undercooling by forcing the chondrule bulk composition to become more magnesian. (If the Fe-loss occurred prior to the chondrule forming event, then isothermal supersaturation is less likely to occur.) Variability of the degree of Fe-loss dominates much of the compositional range of chondrules with Type I chondrules having the lowest Fe- contents. A plausible mechanism for reduction of the silicate droplets in a chondrule forming region, is gas expansion. During heating, the formation of silicate liquid droplets will occur at equilibrium with the "chondrule" vapor phase and any ambient gas. The vapor+gas cloud associated with the heating cycle of chondrule precursors usually will expand more rapidly than the 'cloud' of liquid droplets it contains. As it expands, the fugacity of most species in the gas cloud, including oxygen species, drops, initiating reduction of the entrained droplets. Surface area/volume considerations require that small droplets (<0.5mm) will react much more rapidly than large droplets (>1mm) and as a result a variety of size sorted compositional groups of chondrules may form. Since reduction is initiated on the outer surface of the droplet, simple diffusional arguments indicate that those outer surfaces will experience reduction induced supersaturation first and can precipitate metal and Mg-rich olivine nuclei from which the texture of the chondrule may grow as diffusion limited reduction proceeds inward. Metal grains may act as nucleation sites for olivine in the chondrule or may be lost from the chondrule because of the differential expansion of metal and silicate. The necessity that precipitation begin on the external surfaces of the droplet suggests that textures characterized by annular structures are likely to be formed by this process. The best example is, of course, classic barred olivine, a texture that is approximated by a variety of dendritic textures in cooling experiments. The production of the characteristic annular shell of olivine enclosing the bars in barred olivine chondrules, may be experimentally difficult in current furnaces but its absence in most experiments may also be the result of inappropriate conditions. The final growth of the chondrule texture must involve a suitable cool

Delaney, J. S.

1995-09-01

329

Parents of two-phase flow and theory of "gas-lift"  

NASA Astrophysics Data System (ADS)

This paper gives a brief overview of types of two-phase flow. Subsequently, it deals with their mutual division and problems with accuracy boundaries among particular types. It also shows the case of water flow through a pipe with external heating and the gradual origination of all kinds of flow. We have met it in solution of safety condition of various stages in pressurized and boiling water reactors. In the MSR there is a problem in the solution of gas-lift using helium as a gas and its secondary usage for clearing of the fuel mixture from gaseous fission products. Theory of gas-lift is described.

Zitek, Pavel; Valenta, Vaclav

2014-03-01

330

In situ gas-phase hydrosilylation of plasma-synthesized silicon nanocrystals.  

PubMed

Surface passivation of semiconductor nanocrystals (NCs) is critical in enabling their utilization in novel optoelectronic devices, solar cells, and biological and chemical sensors. Compared to the extensively used liquid-phase NC synthesis and passivation techniques, gas-phase routes provide the unique opportunity for in situ passivation of semiconductor NCs. Herein, we present a method for in situ gas-phase organic functionalization of plasma-synthesized, H-terminated silicon (Si) NCs. Using real-time in situ attenuated total reflection Fourier transform IR spectroscopy, we have studied the surface reactions during hydrosilylation of Si NCs at 160 °C. First, we show that, during gas-phase hydrosilylation of Si NCs using styrene (1-alkene) and acetylene (alkyne), the reaction pathways of the alkenes and alkynes chemisorbing onto surface SiH(x) (x = 1-3) species are different. Second, utilizing this difference in reactivity, we demonstrate a novel pathway to enhance the surface ligand passivation of Si NCs via in situ gas-phase hydrosilylation using the combination of a short-chain alkyne (acetylene) and a long-chain 1-alkene (styrene). The quality of surface passivation is further validated through IR and photoluminescence measurements of Si NCs exposed to air. PMID:21774486

Jariwala, Bhavin N; Dewey, Oliver S; Stradins, Paul; Ciobanu, Cristian V; Agarwal, Sumit

2011-08-01

331

Gas phase water in the surface layer of protoplanetary disks  

E-print Network

Recent observations of the ground state transition of HDO at 464 GHz towards the protoplanetary disk of DM Tau have detected the presence of water vapor in the regions just above the outer disk midplane (Ceccarelli et al 2005). In the absence of non-thermal desorption processes, water should be almost entirely frozen onto the grain mantles and HDO undetectable. In this Letter we present a chemical model that explores the possibility that the icy mantles are photo-desorbed by FUV (6eV water vapor above the disk midplane over the entire disk. Assuming a photo-desorption yield of 10^{-3}, the water abundance in this layer is predicted to be ~ 3 x 10^{-7} and the average H2O column density is ~ 1.6x 10^{15} cm^{-2}. The predictions are very weakly dependent on the details of the model, like the incident FUV radiation field, and the gas density in the disk. Based on this model, we predict a gaseous HDO/H2O ratio in DM Tau of ~1%. In addition, we predict the ground state transition of water at 557 GHz to be undetectable with ODIN and/or HSO-HIFI.

C. Dominik; C. Ceccarelli; D. Hollenbach; M. Kaufman

2005-10-21

332

The interstellar gas-phase chemistry of HCN and HNC  

NASA Astrophysics Data System (ADS)

We review the reactions involving hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) in dark molecular clouds to elucidate new chemical sources and sinks of these isomers. We find that the most important reactions for the HCN-HNC system are dissociative recombination (DR) reactions of HCNH+ (HCNH+ + e-), the ionic CN + H3+, HCN + C+, HCN and HNC reactions with H+/He+/H3+/H3O+/HCO+, the N + CH2 reaction and two new reactions: H + CCN and C + HNC. We test the effect of the new rate constants and branching ratios on the predictions of gas-grain chemical models for dark cloud conditions. The rapid C + HNC reaction keeps the HCN/HNC ratio significantly above 1 as long as the carbon atom abundance remains high. However, the reaction of HCN with H3+ followed by DR of HCNH+ acts to isomerize HCN into HNC when carbon atoms and CO are depleted leading to an HCN/HNC ratio close to or slightly greater than 1. This agrees well with observations in TMC-1 and L134N taking into consideration the overestimation of HNC abundances through the use of the same rotational excitation rate constants for HNC as for HCN in many radiative transfer models.

Loison, Jean-Christophe; Wakelam, Valentine; Hickson, Kevin M.

2014-09-01

333

Surface nanobubbles nucleate microdroplets.  

PubMed

When a hydrophobic solid is in contact with water, surface nanobubbles often form at the interface. They have a lifetime many orders of magnitude longer than expected. Here, we show that they even withstand a temperature increase to temperatures close to the boiling point of bulk water; i.e., they do not nucleate larger bubbles ("superstability"). On the contrary, when the vapor-liquid contact line passes a nanobubble, a liquid film remains around it, which, after pinch-off, results in a microdroplet in which the nanobubbles continue to exist. Finally, the microdroplet evaporates and the nanobubble consequently bursts. Our results support that pinning plays a crucial role for nanobubble stability. PMID:24765973

Zhang, Xuehua; Lhuissier, Henri; Sun, Chao; Lohse, Detlef

2014-04-11

334

Shape and area fluctuation effects on nucleation theory  

NASA Astrophysics Data System (ADS)

In standard nucleation theory, the nucleation process is characterized by computing ??(V), the reversible work required to form a cluster of volume V of the stable phase inside the metastable mother phase. However, other quantities besides the volume could play a role in the free energy of cluster formation, and this will in turn affect the nucleation barrier and the shape of the nucleus. Here we exploit our recently introduced mesoscopic theory of nucleation to compute the free energy cost of a nearly spherical cluster of volume V and a fluctuating surface area A, whereby the maximum of ??(V) is replaced by a saddle point in ??(V, A). Compared to the simpler theory based on volume only, the barrier height of ??(V, A) at the transition state is systematically larger by a few kBT. More importantly, we show that, depending on the physical situation, the most probable shape of the nucleus may be highly non-spherical, even when the surface tension and stiffness of the model are isotropic. Interestingly, these shape fluctuations do not influence or modify the standard Classical Nucleation Theory manner of extracting the interface tension from the logarithm of the nucleation rate near coexistence.

Prestipino, Santi; Laio, Alessandro; Tosatti, Erio

2014-03-01

335

Molecular simulation of crystal nucleation in n-octane melts  

E-print Network

Homogeneous nucleation of the crystal phase in n-octane melts was studied by molecular simulation with a realistic, united-atom model for n-octane. The structure of the crystal phase and the melting point of n-octane were ...

Yi, Peng

336

Nucleating quark droplets in the core of magnetars  

NASA Astrophysics Data System (ADS)

To assess the possibility of homogeneous nucleation of quark matter in magnetars, we investigate the formation of chirally symmetric droplets in a cold and dense environment in the presence of an external magnetic field. As a framework, we use the one-loop effective potential of the two-flavor quark-meson model. Within the thin-wall approximation, we extract all relevant nucleation parameters and provide an estimate for the typical time scales for the chiral phase conversion in magnetized compact star matter. We show how the critical chemical potential, critical radius, correlation length and surface tension are affected, and how their combination to define the nucleation time seems to allow for nucleation of quark droplets in magnetar matter even for not so small values of the surface tension.

Kroff, D.; Fraga, E. S.

2015-01-01

337

Experimental on two sensors combination used in horizontal pipe gas-water two-phase flow  

SciTech Connect

Gas-water two phase flow phenomenon widely exists in production and living and the measurement of it is meaningful. A new type of long-waist cone flow sensor has been designed to measure two-phase mass flow rate. Six rings structure of conductance probe is used to measure volume fraction and axial velocity. The calibration of them have been made. Two sensors have been combined in horizontal pipeline experiment to measure two-phase flow mass flow rate. Several model of gas-water two-phase flow has been discussed. The calculation errors of total mass flow rate measurement is less than 5% based on the revised homogeneous flow model.

Wu, Hao; Dong, Feng [Tianjin Key Laboratory of Process Measurement and Control, School of Electrical Engineering and Automation, Tianjin University, Tianjin (China)

2014-04-11

338

Argon nucleation in a cryogenic nucleation pulse chamber  

NASA Astrophysics Data System (ADS)

Homogeneous nucleation of argon droplets has been measured with a newly designed cryogenic nucleation pulse chamber presented already in a previous paper [Fladerer and Strey, J. Chem. Phys. 124, 16 (2006)]. Here we present the first systematic nucleation onset data for argon measured in a temperature range from 42to58K and for vapor pressures from 0.3to10kPa. For these data we provide an analytical fit function. From the geometry of the optical detection system and the time of nucleation the experimental nucleation-rate range can be estimated. This allows a comparison of the data with the predictions of classical nucleation theory. We found 16-26 orders of magnitude difference between theory and experiment, and a too strong theoretical dependence of the nucleation rate on temperature. A comparison with the self-consistent theory of Girshick and Chiu [J. Chem. Phys. 93, 1273 (1990)] showed improved temperature dependence but still discrepancies of 11-17 orders of magnitude compared to experimental data. The thermodynamically consistent theory of Kashchiev [J. Chem. Phys. 118, 1837 (2003)] was found to agree rather well with experiment in respect to the temperature dependence and to predict rates about 5-7 orders of magnitude below the experimental ones. With the help of the Gibbs-Thomson equation we were able to evaluate the size of the critical nucleus to be 40-80 argon atoms.

Iland, Kristina; Wölk, Judith; Strey, Reinhard; Kashchiev, Dimo

2007-10-01

339

Comparison of the relative importance of helium and vacancy accumulation in void nucleation  

SciTech Connect

Void nucleation in irradiated austenitic stainless steels generally requires the presence of either residual or transmutant gases. Classical nucleation rates are much too low to account for the number of voids observed at temperatures greater than about 450/sup 0/C. An alternate path is generally believed to be responsible for void formation; viz. the growth of gas-stabilized bubbles until they reach a critical size beyond which further gas accumulation is not required to promote growth. Two limiting paths can be envisioned for void nucleation on a population of sub-critical helium/vacancy clusters; one is limited to growth by helium accumulation along and the other to growth by stochastic fluctuations in the vacancy accumulation. As bubbles approach the critical size, stochastic processes could begin to contribute to the void nucleation rate. A comparison is made of nucleation rates along these two limiting paths as a function of the gas content of the clusters.

Stoller, R.E.; Odette, G.R.

1986-06-01

340

Modeling of the dynamics of a gas phase evaporating from the surface of a condensed phase under the effect of concentrated radiation pulses  

Microsoft Academic Search

An algorithm is developed which describes changes with time of the gas phase pressure near the condensate-gas interface due to the effect of concentrated radiation pulses. In the simplest case of a gas transparent to radiation, theoretical results are shown to be in qualitative agreement with experimental data.

P. V. Gerasimenko; V. A. Mazarchenkov; A. D. Suprun; A. M. Fedorchenko

1986-01-01

341

Low liquid loading gas-liquid two-phase flow in near- horizontal pipes  

Microsoft Academic Search

Low liquid loading gas-liquid two-phase flow in near- horizontal pipes has been studied both experimentally and theoretically. A new state-of-the-art, air-oil test facility was designed, constructed and operated. A transparent test section (50.1-cm ID x 19-m long) could be inclined within +\\/-2° from the horizontal. Mineral oil was used as the liquid phase (muL = 5.66 mPa.s, rhoL = 877

Weihong Meng

1999-01-01

342

Fluorometric method for the determination of gas-phase hydrogen peroxide  

Microsoft Academic Search

The fluorometric gas-phase hydrogen peroxide procedure is based on the technique used by Lazrus et. al. for the determination of H2O2 in the liquid phase. The analytical method utilizes the reaction of H2O2 with horseradish peroxidase and p-hydroxphenylacetic acid (POPHA) to form the fluorescent dimer of POPHA. The analytical reaction responds stoichiometrically to both H2O2 and some organic hydroperoxides. To

Gregory L. Kok; Allan L. Lazrus

1986-01-01

343

Silicon clusters produced by femtosecond laser ablation: Non-thermal emission and gas-phase condensation  

E-print Network

Neutral silicon clusters Si_n (up to n = 7) and their cations Si_n+ (up to n = 10) have been produced by femtosecond laser ablation of bulk silicon in vacuum and investigated using time-of-flight mass spectrometry. Two populations of the Si_n+ clusters with different velocity and abundance distributions in the ablation plume have been clearly distinguished. Possible mechanisms of cluster formation (Coulomb explosion, gas-phase condensation, phase explosion) are discussed.

Bulgakov, A V; Ozerov, I; Bulgakov, Alexander V.; Ozerov, Igor; ccsd-00001265, ccsd

2004-01-01

344

Flow field simulation of gas-water two phase flow in annular channel  

NASA Astrophysics Data System (ADS)

The gas-water two-phase flow is very common in the industrial processes. the deep understanding of the two-phase flow state is to achieve the production equipment design and safe operation. In the measurement of gas-water two-phase flow, the differential pressure sensor is widely used, and some measurement model of multiphase flow have been concluded. The differential pressure is generated when fluid flowing through the throttling components to calculate flow rate. This paper mainly focuses on two points: 1. The change rule of the parameters include velocity, pressure, phase fraction as the change of time, when the phase inlet velocity is given. 2. Analysis the distribution of the parameters above-mentioned at a certain moment under the condition of different water inlet velocity. Three-dimensional computational fluid dynamics (CFD) approach was used to simulate gas-water two-phase flow fluid in the annular channel, which is composed of horizontal pipe and long- waist cone sensor. The simulation results were obtained from FLUENT software.

Ji, Pengcheng; Dong, Feng

2014-04-01

345

MOLECULAR SPECTROSCPY AND REACTIONS OF ACTINIDES IN THE GAS PHASE AND CRYOGENIC MATRICES  

SciTech Connect

In this chapter we review the spectroscopic data for actinide molecules and the reaction dynamics for atomic and molecular actinides that have been examined in the gas phase or in inert cryogenic matrices. The motivation for this type of investigation is that physical properties and reactions can be studied in the absence of external perturbations (gas phase) or under minimally perturbing conditions (cryogenic matrices). This information can be compared directly with the results from high-level theoretical models. The interplay between experiment and theory is critically important for advancing our understanding of actinide chemistry. For example, elucidation of the role of the 5f electrons in bonding and reactivity can only be achieved through the application of experimentally verified theoretical models. Theoretical calculations for the actinides are challenging due the large numbers of electrons that must be treated explicitly and the presence of strong relativistic effects. This topic has been reviewed in depth in Chapter 17 of this series. One of the goals of the experimental work described in this chapter has been to provide benchmark data that can be used to evaluate both empirical and ab initio theoretical models. While gas-phase data are the most suitable for comparison with theoretical calculations, there are technical difficulties entailed in generating workable densities of gas-phase actinide molecules that have limited the range of species that have been characterized. Many of the compounds of interest are refractory, and problems associated with the use of high temperature vapors have complicated measurements of spectra, ionization energies, and reactions. One approach that has proved to be especially valuable in overcoming this difficulty has been the use of pulsed laser ablation to generate plumes of vapor from refractory actinide-containing materials. The vapor is entrained in an inert gas, which can be used to cool the actinide species to room temperature or below. For many spectroscopic measurements, low temperatures have been achieved by co-condensing the actinide vapor in rare gas or inert molecule host matrices. Spectra recorded in matrices are usually considered to be minimally perturbed. Trapping the products from gas-phase reactions that occur when trace quantities of reactants are added to the inert host gas has resulted in the discovery of many new actinide species. Selected aspects of the matrix isolation data were discussed in chapter 17. In the present chapter we review the spectroscopic matrix data in terms of its relationship to gas-phase measurements, and update the description of the new reaction products found in matrices to reflect the developments that have occurred during the past two years. Spectra recorded in matrix environments are usually considered to be minimally perturbed, and this expectation is borne out for many closed shell actinide molecules. However, there is growing evidence that significant perturbations can occur for open shell molecules, resulting in geometric distortions and/or electronic state reordering. Studies of actinide reactions in the gas phase provide an opportunity to probe the relationship between electronic structure and reactivity. Much of this work has focused on the reactions of ionic species, as these may be selected and controlled using various forms of mass spectrometry. As an example of the type of insight derived from reaction studies, it has been established that the reaction barriers for An+ ions are determined by the promotion energies required to achieve the 5fn6d7s configuration. Gas-phase reaction studies also provide fundamental thermodynamic properties such as bond dissociation and ionization energies. In recent years, an increased number of gas-phase ion chemistry studies of bare (atomic) and ligated (molecular) actinide ions have appeared, in which relevant contributions to fundamental actinide chemistry have been made. These studies were initiated in the 1970's and carried out in an uninterrupted way over the course of the past three d

Heaven, Michael C.; Gibson, John K.; Marcalo, Joaquim

2009-02-01

346

In vivo bubble nucleation probability in sheep brain tissue  

NASA Astrophysics Data System (ADS)

Gas nuclei exist naturally in living bodies. Their activation initiates cavitation activity, and is possible using short ultrasonic excitations of high amplitude. However, little is known about the nuclei population in vivo, and therefore about the rarefaction pressure required to form bubbles in tissue. A novel method dedicated to in vivo investigations was used here that combines passive and active cavitation detection with a multi-element linear ultrasound probe (4-7 MHz). Experiments were performed in vivo on the brain of trepanated sheep. Bubble nucleation was induced using a focused single-element transducer (central frequency 660 kHz, f-number = 1) driven by a high power (up to 5 kW) electric burst of two cycles. Successive passive recording and ultrafast active imaging were shown to allow detection of a single nucleation event in brain tissue in vivo. Experiments carried out on eight sheep allowed statistical studies of the bubble nucleation process. The nucleation probability was evaluated as a function of the peak negative pressure. No nucleation event could be detected with a peak negative pressure weaker than -12.7 MPa, i.e. one order of magnitude higher than the recommendations based on the mechanical index. Below this threshold, bubble nucleation in vivo in brain tissues is a random phenomenon.

Gateau, J.; Aubry, J.-F.; Chauvet, D.; Boch, A.-L.; Fink, M.; Tanter, M.

2011-11-01

347

Formation routes of interstellar glycine involving carboxylic acids: possible favoritism between gas and solid phase.  

PubMed

Despite the extensive search for glycine (NH?CH?COOH) and other amino acids in molecular clouds associated with star-forming regions, only upper limits have been derived from radio observations. Nevertheless, two of glycine's precursors, formic acid and acetic acid, have been abundantly detected. Although both precursors may lead to glycine formation, the efficiency of reaction depends on their abundance and survival in the presence of a radiation field. These facts could promote some favoritism in the reaction pathways in the gas phase and solid phase (ice). Glycine and these two simplest carboxylic acids are found in many meteorites. Recently, glycine was also observed in cometary samples returned by the Stardust space probe. The goal of this work was to perform theoretical calculations for several interstellar reactions involving the simplest carboxylic acids as well as the carboxyl radical (COOH) in both gas and solid (ice) phase to understand which reactions could be the most favorable to produce glycine in interstellar regions fully illuminated by soft X-rays and UV, such as star-forming regions. The calculations were performed at four different levels for the gas phase (B3LYP/6-31G*, B3LYP/6-31++G**, MP2/6-31G*, and MP2/6-31++G**) and at MP2/6-31++G** level for the solid phase (ice). The current two-body reactions (thermochemical calculation) were combined with previous experimental data on the photodissociation of carboxylic acids to promote possible favoritism for glycine formation in the scenario involving formic and acetic acid in both gas and solid phase. Given that formic acid is destroyed more in the gas phase by soft X-rays than acetic acid is, we suggest that in the gas phase the most favorable reactions are acetic acid with NH or NH?OH. Another possible reaction involves NH?CH? and COOH, one of the most-produced radicals from the photodissociation of acetic acid. In the solid phase, we suggest that the reactions of formic acid with NH?CH or NH?CH?OH are the most favorable from the thermochemical point of view. PMID:22066498

Pilling, Sergio; Baptista, Leonardo; Boechat-Roberty, Heloisa M; Andrade, Diana P P

2011-11-01

348

A modeling and experimental study of flue gas desulfurization in a dense phase tower.  

PubMed

We used a dense phase tower as the reactor in a novel semi-dry flue gas desulfurization process to achieve a high desulfurization efficiency of over 95% when the Ca/S molar ratio reaches 1.3. Pilot-scale experiments were conducted for choosing the parameters of the full-scale reactor. Results show that with an increase in the flue gas flow rate the rate of the pressure drop in the dense phase tower also increases, however, the rate of the temperature drop decreases in the non-load hot gas. We chose a water flow rate of 0.6 kg/min to minimize the approach to adiabatic saturation temperature difference and maximize the desulfurization efficiency. To study the flue gas characteristics under different processing parameters, we simulated the desulfurization process in the reactor. The simulated data matched very well with the experimental data. We also found that with an increase in the Ca/S molar ratio, the differences between the simulation and experimental data tend to decrease; conversely, an increase in the flue gas flow rate increases the difference; this may be associated with the surface reactions caused by collision, coalescence and fragmentation between the dispersed phases. PMID:21377795

Chang, Guanqin; Song, Cunyi; Wang, Li

2011-05-15

349

Climate Impacts of Ice Nucleation  

NASA Technical Reports Server (NTRS)

Several different ice nucleation parameterizations in two different General Circulation Models (GCMs) are used to understand the effects of ice nucleation on the mean climate state, and the Aerosol Indirect Effects (AIE) of cirrus clouds on climate. Simulations have a range of ice microphysical states that are consistent with the spread of observations, but many simulations have higher present-day ice crystal number concentrations than in-situ observations. These different states result from different parameterizations of ice cloud nucleation processes, and feature different balances of homogeneous and heterogeneous nucleation. Black carbon aerosols have a small (0.06 Wm(exp-2) and not statistically significant AIE when included as ice nuclei, for nucleation efficiencies within the range of laboratory measurements. Indirect effects of anthropogenic aerosols on cirrus clouds occur as a consequence of increasing anthropogenic sulfur emissions with different mechanisms important in different models. In one model this is due to increases in homogeneous nucleation fraction, and in the other due to increases in heterogeneous nucleation with coated dust. The magnitude of the effect is the same however. The resulting ice AIE does not seem strongly dependent on the balance between homogeneous and heterogeneous ice nucleation. Regional effects can reach several Wm2. Indirect effects are slightly larger for those states with less homogeneous nucleation and lower ice number concentration in the base state. The total ice AIE is estimated at 0.27 +/- 0.10 Wm(exp-2) (1 sigma uncertainty). This represents a 20% offset of the simulated total shortwave AIE for ice and liquid clouds of 1.6 Wm(sup-2).

Gettelman, Andrew; Liu, Xiaohong; Barahona, Donifan; Lohmann, Ulrike; Chen, Celia

2012-01-01

350

Gas pressure on the surface of condensed phase in a resonance radiation field  

Microsoft Academic Search

The influence of resonance radiation on the pressure exerted by gas on the surface of a condensed phase is studied. The effects, which are associated with a change in the recoil pressure of molecules escaping from the surface in a radiation field, are considered. Combined manifestation of thermal and resonance effects is analyzed, as well as the influence of a

V. V. Levdansky

1999-01-01

351

Conformational effects in sugar ions: spectroscopic investigations in the gas phase and in solution  

E-print Network

Conformational effects in sugar ions: spectroscopic investigations in the gas phase and in solution of sugars with a positively charged substituent at their anomeric centre, C-1, which display in solution in an ionic sugar, per-acetylated a-D-glucopyranosyl pyridinium, which reversed the axial (and equatorial

Davis, Ben G.

352

Evaluated Gas Phase Basicities and Proton Affinities of Molecules; Heats of Formation of Protonated Molecules  

Microsoft Academic Search

The available data on gas phase basicities and proton affinities of molecules are compiled and evaluated. Tables giving the molecules ordered (1) according to proton affinity and (2) according to empirical formula, sorted alphabetically are provided. The heats of formation of the molecules and the corresponding protonated species are also listed.

Sharon G. Lias; Joel F. Liebman; Rhoda D. Levin

1984-01-01

353

SELECTIVE OXIDATION OF ALCOHOLS IN GAS PHASE USING LIGHT-ACTIVATED TITANIUM DIOXIDE  

EPA Science Inventory

Selective oxidations of various primary and secondary alcohols were studied in a gas phase photochemical reactor using immobilized TiO2 catalyst. An annular photoreactor was used at 463K with an average contact time of 32sec. The system was found to be specifically suited for the...

354

Molecular Orbital Studies of Titanium Nitride Chemical Vapor Deposition: Gas Phase Complex Formation,  

E-print Network

Molecular Orbital Studies of Titanium Nitride Chemical Vapor Deposition: Gas Phase Complex Received June 6, 2000 The chemical vapor deposition (CVD) of titanium nitride can be carried out with TiCl4 Titanium nitride thin films have a variety of proper- ties, such as extreme hardness, high chemical

Schlegel, H. Bernhard

355

Electronic Structure and Spectra of Catechol and Alizarin in the Gas Phase and Attached to Titanium  

E-print Network

Electronic Structure and Spectra of Catechol and Alizarin in the Gas Phase and Attached to Titanium and alizarin molecules upon binding to titanium. Catechol and alizarin are similar chromophores with analogous electronic spectra in the free state. Binding alizarin to titanium red-shifts the spectrum. The binding

356

Infrared Spectroscopy of Cationized Arginine in the Gas Phase: Direct Evidence for the Transition from  

E-print Network

Infrared Spectroscopy of Cationized Arginine in the Gas Phase: Direct Evidence for the Transition methyl ester (ArgOMe) are investigated with infrared spectroscopy and ab initio calculations. Infrared to the nonzwitterionic form is directly related to proton affinity.14,15 This relationship can be far less direct for non

Cohen, Ronald C.

357

METHODS FOR SIMULATING GAS PHASE SO2 OXIDATION IN ATMOSPHERIC MODELS  

EPA Science Inventory

Two different approaches are presented for simulating gas phase sulfur dioxide oxidation in atmospheric models. The first approach was to develop an empirical relationship based on rate data collected at four coal-fired power plants during 11 separate studies. Cosine functions we...

358

Self-Assembly of Well-Defined Nanostructures by Hydrogen Bonding in the Gas Phase  

Microsoft Academic Search

Micrometer-long nanobelt and nanowires from deposition of perylenediimide (PTCDI) and naphthalenediimide (NPDI) in glass substrates from the gas phase were demonstrated. The electron diffraction pattern of PTCDI shows that the PTCDI molecules are oriented with their long axis perpendicular to the belt and the - stacking direction parallel to the belt. No crystal structure of the NPDI nanowires was observed.

Hai-Feng Ji; Ravish Majithia; Xin Yang; Xiaohe Xu; Karren Leslie More

2008-01-01

359

Methylation of 2-Naphthol Using Dimethyl Carbonate under Continuous-Flow Gas-Phase Conditions  

ERIC Educational Resources Information Center

This experiment investigates the methylation of 2-naphthol with dimethyl carbonate. The volatility of the substrates, products, and co-products allows the reaction to be performed using a continuous-flow gas-phase setup at ambient pressure. The reaction uses catalytic quantities of base, achieves high conversion, produces little waste, and…

Tundo, Pietro; Rosamilia, Anthony E.; Arico, Fabio

2010-01-01

360

SPECIATION OF GAS-PHASE AND FINE PARTICLE EMISSIONS FROM BURNING OF FOLIAR FUELS: JOURNAL ARTICLE  

EPA Science Inventory

NRMRL-RTP-P- 620 Hays**, M.D., Geron*, C.D., Linna**, K.J., Smith*, N.D., and Schauer, J.J. Speciation of Gas-Phase and Fine Particle Emissions from Burning of Foliar Fuels. Submitted to: Environmental Science & Technology EPA/600/J-02/234, http://pubs.acs.org/journals/esthag/...

361

CONTROL OF UTILITY BOILER AND GAS TURBINE POLLUTANT EMISSIONS BY COMBUSTION MODIFICATION--PHASE II  

EPA Science Inventory

The report gives results of Phase II of a field study to assess the applicability of combustion modification (CM) techniques to control NOx and other pollutant emissions from utility boilers and gas turbines without causing deleterious side effects. Comprehensive, statistically d...

362

Carbonic Anhydrase-Inhibitor Binding: From Solution to the Gas Phase  

E-print Network

Carbonic Anhydrase-Inhibitor Binding: From Solution to the Gas Phase Qinyuan Wu,,§ Jinming Gao stabilities of nonco- valent complexes between bovine carbonic anhydrase II (BCAII, EC 4.2.1.1) and para systems due to the stability of carbonic anhydrase (CA) and its well characterized structure and ligand

Gao, Jinming

363

Probing the Energetics of Dissociation of Carbonic Anhydrase-Ligand Complexes in the Gas Phase  

E-print Network

Probing the Energetics of Dissociation of Carbonic Anhydrase-Ligand Complexes in the Gas Phase comparing the stability of carbonic anhydrase-benzenesulfonamide complexes in the presence and absence mass spectrometry (ESI-FTICR-MS) to study the relative stabilities of noncovalent complexes of carbonic

Prentiss, Mara

364

Carbonic anhydrase-inhibitor binding: From solution to the gas phase  

SciTech Connect

In this report, we compare the kinetic stabilities of noncovalent complexes between bovine carbonic anhydrase II(BCAII, EC 4.2.1.1) and para-substituted benzenesulfonamide inhibitors in the gas phase and in solution. These BCAII-inhibitor systems are attractive model systems due to the stability of carbonic anhydrase (CA) and its well characterized structure and ligand complexes, providing a basis for inferences regarding the protein structure in the gas phase and its ligand interactions. CA is a roughly spherical Zn(II) metalloenzyme having a conical binding pocket which catalyzes the hydration of CO{sub 2} to bicarbonate. A large body of data correlate structures of sulfonamide ligands with their binding constants to CA. A set of eight inhibitors was selected for this study, covering a wide range of binding affinities and varying in the length of their tails and aromatic content. The results demonstrate that relative stabilities of BCAII-inhibitor complexes differ substantially between the gas and liquid phases and also show the dominant role of polar surface interactions in the gas phase. 12 refs., 1 fig., 1 tab.

Wu, Q.; Bruce, J.E.; Smith, R.D. [Pacific Northwest National Lab., Richland, WA (United States)] [Pacific Northwest National Lab., Richland, WA (United States); Gao, J.; Joseph-McCarthy, D.; Sigal, G.B.; Whitesides, G.M. [Harvard Univ., Cambridge, MA (United States)] [Harvard Univ., Cambridge, MA (United States)

1997-02-05

365

CHEMICAL TRANSFORMATION MODULES FOR EULERIAN ACID DEPOSITION MODELS. VOLUME 1. THE GAS-PHASE CHEMISTRY  

EPA Science Inventory

This study focuses on the review and evaluation of mechanistic and kinetic data for the gas-phase reactions that lead to the production of acidic substances in the environment. A master mechanism is designed that treats oxides, sulfur dioxide, ozone, hydrogen peroxide, ammonia, t...

366

Ozonation of coal vitrinites of different metamorphism degrees in gas and liquid phases  

SciTech Connect

The comparative analysis of the dynamics of accumulation of oxygen-containing groups in coals of different metamorphism degrees under their ozonation in the gas phase and in chloroform has been performed. The coals of the middle stage of metamorphism demonstrate the highest reactivity. The ozonation in chloroform proceeds with a higher intensity.

S.A. Semenova; Y.F. Patrakov [Russian Academy of Sciences, Kemerovo (Russian Federation). Institute of Coal and Coal Chemistry, Siberian Division

2007-02-15

367

Molecular Orbital Studies of Zinc Oxide Chemical Vapor Deposition: Gas-Phase Hydrolysis of Diethyl Zinc,  

E-print Network

region.1,2 Doping with indium, gallium, or aluminum improves these properties.3-5 These characteristicsMolecular Orbital Studies of Zinc Oxide Chemical Vapor Deposition: Gas-Phase Hydrolysis of Diethyl deposition of zinc oxide thin films can be carried out with diethyl zinc and water vapor. The present study

Schlegel, H. Bernhard

368

A Model of Gas-Phase Transport During the Initial Stages of Sintering of Silicon Carbide  

E-print Network

A Model of Gas-Phase Transport During the Initial Stages of Sintering of Silicon Carbide Anil Kaza used as an additive to silicon carbide powder, is thought to facilitate densification during sintering pressureless sintering of silicon carbide (SiC) was first discovered by Prochazka in 1977,1 using boron

Matthewson, M. John

369

ADVANCED OXIDATION AND REDUCTION PROCESSES IN THE GAS PHASE USING NON-THERMAL PLASMAS  

EPA Science Inventory

In the past several years interest in gas-phase pollution control has increased, arising from a larger body of regulations and greater respect for the environment. Advanced oxidation technologies (AOTs), historically used to treat recalcitrant water pollutants via hydroxyl-radica...

370

A Fortran computer code package for the evaluation of gas-phase, multicomponent transport properties  

Microsoft Academic Search

This report documents a Fortran computer code package that is used for the evaluation of gas-phase multicomponent viscosities, thermal conductivities, diffusion coefficients, and thermal diffusion coefficients. The package is in two parts. The first is a preprocessor that computes polynomial fits to the temperature dependent parts of the pure species viscosities and binary diffusion coefficients. The coefficients of these fits

Robert J. Kee; Graham Dixon-Lewis; Jürgen Warnatz; Michael E. Coltrin; J. A. Miller

1986-01-01

371

Sequential flow injection analysis of ammonium and nitrate using gas phase molecular absorption spectrometry  

Microsoft Academic Search

A flow injection method on the basis of gas phase molecular absorption is described for the sequential determination of ammonium and nitrate. Two hundred microliters of sample solution is injected into the flow line. For ammonium determination, the sample zone is directed to a line in which reacts with NaOH (13M) and produces ammonia. But for nitrate determination, the sample

B. Haghighi; S. Farrokhi Kurd

2004-01-01

372

Molecular structures of gas-phase polyatomic molecules determined by spectroscopic methods  

Microsoft Academic Search

Spectroscopic data related to the structures of polyatomic molecules in the gas phase have been reviewed, critically evaluated, and compiled. All reported bond distances and angles have been classified as equilibrium (re), average (rz), substitution (rs), or effective (ro) parameters, and have been given a quality rating which is a measure of the parameter uncertainty. The surveyed literature includes work

Marlin D. Harmony; Victor W. Laurie; Robert L. Kuczkowski; R. H. Schwendeman; D. A. Ramsay; Frank J. Lovas; Walter J. Lafferty; Arthur G. Maki

1979-01-01

373

ECO LOGIC INTERNATIONAL GAS-PHASE CHEMICAL REDUCTION PROCESS - THE THERMAL DESORPTION UNIT - APPLICATIONS ANALYSIS REPORT  

EPA Science Inventory

This report details the Superfund Innovative Technology Evaluation of the Eco Logic International's gas-phase chemical reduction process, with an emphasis on their thermal desorption unit. he Eco Logic process employs a high temperature reactor filled with hydrogen as a means to ...

374

ECO LOGIC INTERNATIONAL GAS-PHASE CHEMICAL REDUCTION PROCESS - THE THERMAL DESORPTION UNIT - APPLICATIONS ANALYSIS REPORT  

EPA Science Inventory

ELI ECO Logic International, Inc.'s Thermal Desorption Unit (TDU) is specifically designed for use with Eco Logic's Gas Phase Chemical Reduction Process. The technology uses an externally heated bath of molten tin in a hydrogen atmosphere to desorb hazardous organic compounds fro...

375

Magnetizabilities and Nuclear Shielding Constants of the Fluoromethanes in the Gas Phase and Solution  

E-print Network

Magnetizabilities and Nuclear Shielding Constants of the Fluoromethanes in the Gas Phase The effects of a dielectric medium on the magnetizabilities and nuclear shielding constants an important role, as is clearly demonstrated for the magnetizability of the CH3F molecule where

Helgaker, Trygve

376

Solid and gas phase inventory of the low mass protostar Elias 29 (ae Oph)  

E-print Network

CHAPTER 7 Solid and gas phase inventory of the low mass protostar Elias 29 (ae Oph) To be submitted ) Class I protostellar object Elias 29 in the ae Ophiuchi molecular cloud. It provides a unique amount outflow. In many aspects, Elias 29 resembles the Herbig Ae star AB Aur, although Elias 29 is less evolved

Boogert, Adwin

377

Gas-Phase Tropospheric Chemistry of Volatile Organic Compounds: 1. Alkanes and Alkenes  

Microsoft Academic Search

Literature data (through mid-1996) concerning the gas-phase reactions of alkanes and alkenes (including isoprene and monoterpenes) leading to their first generation products are reviewed and evaluated for tropospheric conditions. The recommendations of the most recent IUPAC evaluation [J. Phys. Chem. Ref. Data, 26, No. 3 (1997)] are used for the ?C3 organic compounds, unless more recent data necessitates reevaluation. The

Roger Atkinson

1997-01-01

378

Adapting gas-phase electron scattering R -matrix calculations to a condensed-matter environment  

Microsoft Academic Search

We investigate how gas phase R -matrix calculations for electron collisions with the water molecule can be efficiently used in a condensed environment. The electron band structure of cubic ice being fairly well studied, we try to reproduce it using a generalization of the Korringa-Kohn-Rostoker band calculation method. We find two cutoffs have to be applied to the R -matrix

Laurent Caron; D. Bouchiha; J. D. Gorfinkiel; L. Sanche

2007-01-01

379

Gas-Phase Ignition of Premixed Fuel by Catalytic Bodies in Stagnation Flow  

Microsoft Academic Search

Abstract-In this paper the gas-phase ignition of a premixed fuel by catalytic surfaces of finite sizes is studied, using asymptotic methods. The flow selected for this analysis was the planar stagnation flow. The ignition is generated by a finite thickness plate, the lower surface of which is at a uniform high temperature. This study considers two principal cases: the slightly

C. TREVIÑO

1983-01-01

380

Evidence for Unfolding and Refolding of Gas-Phase Cytochrome Ions in a Paul Trap  

Microsoft Academic Search

The folding pathways of gas-phase cytochrome c ions produced by electrospray ionization have been studied by an ion trapping\\/ion mobility technique that allows conformations to be examined over extended timescales (10 ms to 10 s). The results show that the 9 charge state emerges from solution as a compact structure and then rapidly unfolds into several substantially more open structures,

Ethan R. Badman; Sunnie Myung; David E. Clemmer

2005-01-01

381

Bond and site selectivity in dissociative electron attachment to gas phase and condensed phase ethanol and trifluoroethanol.  

PubMed

The formation of negative ions following electron impact to ethanol (CH(3)CH(2)OH) and trifluoroethanol (CF(3)CH(2)OH) is studied in the gas phase by means of a crossed electron-molecular beam experiment and in the condensed phase via Electron Stimulated Desorption (ESD) of fragment ions from the corresponding molecular films under UHV conditions. Gas phase ethanol exhibits two pronounced resonances, located at 5.5 eV and 8.2 eV, associated with a remarkable selectivity in the decomposition of the precursor ion. While the low energy resonance exclusively decomposes into O(-), that at higher energy generates OH(-) and a comparatively small signal of [CH(3)CH(2)O](-) due to the loss of a neutral hydrogen. CF(3)CH(2)OH shows a completely different behaviour, as now an intense feature at 1.7 eV appears associated with the loss of a neutral hydrogen atom exclusively occurring at the O site. The H(-) formation from the gas phase compounds is below the detection limit of the present experiment, while in ESD from 3 MonoLayer (ML) films of CH(3)CH(2)OH and CF(3)CH(2)OH the most intense fragment is H(-), appearing from a broad resonant feature between 7 and 12 eV. With CF(3)CH(2)OH, by using the isotopically-labelled analogues CF(3)CD(2)OH and CF(3)CH(2)OD it can be shown that this feature consists of two resonances, one located at 8 eV leading to H(-)/D(-) loss from the O site and a second resonance located at 10 eV leading to the loss of H(-)/D(-) from the CH(2) site. PMID:17664966

Orzol, Mario; Martin, Isabel; Kocisek, Jaroslav; Dabkowska, Iwona; Langer, Judith; Illenberger, Eugen

2007-07-14

382

Nucleation and crystal growth in binary systems  

NASA Astrophysics Data System (ADS)

A time-dependent nucleation of spherical crystals accompanied by their growth in metastable binary melts at the intermediate stage of phase transitions is analyzed. Two integro-differential models of governing equations are solved analytically for size- and supercooling-dependent growth rates and different expressions for the nucleation frequency. Two important cases of the Weber-Volmer-Frenkel-Zel’dovich and Meirs nucleation kinetic mechanisms are considered. The first model of crystal growth without fluctuating rates is completely solved by means of the saddle-point method. The exact analytical solution of the second model, taking into account the presence of fluctuations in particle growth rates, is found in a parametric form. The present theory describing binary systems generalizes the theories describing single-component systems recently developed in the absence (Alexandrov and Malygin 2013 J. Phys. A: Math. Theor. 46 455101) and in the presence (Alexandrov and Malygin 2014 Modelling Simul. Mater. Sci. Eng. 22 015003) of fluctuations in crystal growth rates.

Alexandrov, D. V.

2014-03-01

383

Studies of cluster-assembled materials: From gas phase to condensed phase  

NASA Astrophysics Data System (ADS)

Clusters, defined as "a number of similar things that occur together" in Webster's dictionary, has different meanings depending on the given subject. To physicists and chemists, the word cluster means "a group of atoms or molecules formed by interactions ranging from very weak van der Waals interactions to strong ionic bonds." Unlike molecules, which are made by nature and are stable under ambient conditions, clusters discovered in a laboratory are often metastable. Molecules have specific stoichiometry, whereas the cluster's composition can usually be altered atom by atom. Thus, clusters can be taken as intrinsically "artificial molecules" with considerably more tunabilities in their properties. Research into the relative stability and instability of clusters has in recent years become a very active research area, especially following the study by Khanna and Castleman that first suggested that by varying size and composition, clusters can expand the periodic table to the 3 rd-dimension; that is, clusters can mimic the chemistry of atoms and may, therefore, be used as the building blocks of new materials. The discovery of Met-Cars has drawn worldwide interests and has been actively investigated by researchers from a variety of fields, including physics, chemistry and material science. However, the unsuccessful search for a solvent capable of isolating Met-Cars has impeded progress in characterizing the material in the condensed state and, hence, limited its potential applications as a novel nanoscale material. An alternative method involving the deposition of mass-gated species and the subsequent structural investigation via Transmission Electron Microscopy (TEM) has been employed. With particularly interesting results, soft-landed deposits of zirconium Met-Cars were found to form a face-centered-cubic (FCC) structure with a lattice parameter ˜ 15A. The production of Met-Cars is conducted with the direct laser vaporization (DLV) of metal/graphite composite pellets. After being mass gated in a reflectron equipped time-of-flight mass spectrometer (TOF-MS) and deposited onto TEM grids, the resultant specimens can be loaded onto high-resolution TEM investigation via electron diffraction. In conclusion, soft-landing of mass selected clusters has been shown to be a successful approach to obtain structural information on Zr-Met-Car cluster-assembled materials collected from the gas phase. TEM images indicate the richness of the morphologies associated with these cluster crystals. However, passivation methods are expected to be examined further to overcome the limited stabilities of these novel clusters. From this initial study, it's shown the promising opportunity to study other Met-Cars species and more cluster-based materials. Experimental results of reactions run with a solvothermal synthesis method obtained while searching for new Zr-C cluster assembled materials, are reported. One unexpected product in single crystal form was isolated and tentatively identified by X-ray diffraction to be [Zr6i O(OH)O12·2(Bu)4], with space group P2 1/n and lattice parameters of a = 12.44 A, b = 22.06 A, c = 18.40 A, alpha = 90°, beta = 105°, gamma = 90°, V = 4875 A3 and R 1 = 3.15% for the total observed data (I ? 2 sigma I) and oR2 = 2.82%. This novel hexanuclear Zr(IV)-oxo-hydroxide cluster anion may be the first member in polyoxometalates class with metal atoms from the IVB group and having Oh symmetry. Alternatively, it may be the first member in {[(Zr6Z)X 12]X6}m- class with halides replaced by oxo- and hydroxyl groups and with an increased oxidation state of Zr. It is predicted to bear application potentials directed by both families. This work could suggest a direction in which the preparation of Zr-C cluster-assembled materials in a liquid environment may be eventually fulfilled. 1,3-Bis(diethylphosphino)propane (depp) protected small gold clusters are studied via multiple techniques, including Electrospray Ionization Mass Spectrometry (ESI-MS), Ultraviolet-Visible Spectroscopy (Uv-Vis), Nuclear

Gao, Lin

384

Lattice model theory of the equation of state covering the gas, liquid, and solid phases  

NASA Technical Reports Server (NTRS)

The three stable states of matter and the corresponding phase transitions were obtained with a single model. Patterned after Lennard-Jones and Devonshires's theory, a simple cubic lattice model containing two fcc sublattices (alpha and beta) is adopted. The interatomic potential is taken to be the Lennard-Jones (6-12) potential. Employing the cluster variation method, the Weiss and the pair approximations on the lattice gas failed to give the correct phase diagrams. Hybrid approximations were devised to describe the lattice term in the free energy. A lattice vibration term corresponding to a free volume correction is included semi-phenomenologically. The combinations of the lattice part and the free volume part yield the three states and the proper phase diagrams. To determine the coexistence regions, the equalities of the pressure and Gibbs free energy per molecule of the coexisting phases were utilized. The ordered branch of the free energy gives rise to the solid phase while the disordered branch yields the gas and liquid phases. It is observed that the triple point and the critical point quantities, the phase diagrams and the coexistence regions plotted are in good agreement with the experimental values and graphs for argon.

Bonavito, N. L.; Tanaka, T.; Chan, E. M.; Horiguchi, T.; Foreman, J. C.

1975-01-01

385

Evidence for ?-helices in the gas phase: a case study using Melittin from honey bee venom.  

PubMed

Gas phase methodologies are increasingly used to study the structure of proteins and peptides. A challenge to the mass spectrometrist is to preserve the structure of the system of interest intact and unaltered from solution into the gas phase. Small peptides are very flexible and can present a number of conformations in solution. In this work we examine Melittin a 26 amino acid peptide that forms the active component of honey bee venom. Melittin is haemolytic and has been shown to form an ?-helical tetrameric structure by X-ray crystallography [M. Gribskov et al., The RCSB Protein Data Bank, 1990] and to be helical in high concentrations of methanol. Here we use ion mobility mass spectrometry, molecular dynamics and gas-phase HDX to probe its structure in the gas phase and specifically interrogate whether the helical form can be preserved. All low energy calculated structures possess some helicity. In our experiments we examine the peptide following nano-ESI from solutions with varying methanol content. Ion mobility gives collision cross sections (CCS) that compare well with values found from molecular modelling and from other reported structures, but with inconclusive results regarding the effect of solvent. There is only a slight increase in CCS with charge, showing minimal coloumbically driven unfolding. HDX supports preservation of some helical content into the gas phase and again shows little difference in the exchange rates of species sprayed from different solvents. The [M + 3H](3+) species has two exchanging populations both of which exhibit faster exchange rates than observed for the [M + 2H](2+) species. One interpretation for these results is that the time spent being analysed is sufficient for this peptide to form a helix in the 'ultimate' hydrophobic environment of a vacuum. PMID:21701716

Florance, Hannah V; Stopford, Andrew P; Kalapothakis, Jason M; McCullough, Bryan J; Bretherick, Andrew; Barran, Perdita E

2011-09-01

386

Phase diagram of a two-component Fermi gas with resonant interactions  

E-print Network

The pairing of fermions is at the heart of superconductivity and superfluidity. The recent experimental realization of strongly interacting atomic Fermi gases has opened a new, controllable way to study novel forms of pairing and superfluidity. A major controversial issue has been the stability of superfluidity against an imbalance between the two spin components when the fermions interact resonantly. Here we present the phase diagram of a spin-polarized Fermi gas of $^6$Li atoms at unitarity, mapping out the superfluid phase versus temperature and density imbalance. Using tomographic techniques, we reveal spatial discontinuities in the spin polarization, the signature of a first-order superfluid-to-normal phase transition, which disappears at a tricritical point where the nature of the phase transition changes from first-order to second-order. At zero temperature, there is a quantum phase transition from a fully-paired superfluid to a partially-polarized normal gas. These observations and the implementation of an in situ ideal gas thermometer provide quantitative tests of theoretical calculations on the stability of resonant superfluidity.

Yong-il Shin; Christian H. Schunck; Andre Schirotzek; Wolfgang Ketterle

2007-09-19

387

Gas-Phase Transformation of Phosphatidylcholine Cations to Structurally Informative Anions via Ion/Ion Chemistry  

PubMed Central

Gas-phase transformation of synthetic phosphatidylcholine (PC) monocations to structurally informative anions is demonstrated via ion/ion reactions with doubly deprotonated 1,4-phenylenedipropionic acid (PDPA). Two synthetic PC isomers, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (PC16:0/18:1) and 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (PC18:1/16:0) were subjected to this ion/ion chemistry. The product of the ion/ion reaction is a negatively charged complex, [PC+PDPA-H]?. Collisional activation of the long-lived complex causes transfer of a proton and methyl cation to PDPA, generating [PC-CH3]?. Subsequent collisional activation of the demethylated PC anions produces abundant fatty acid carboxylate anions and low abundance acyl neutral losses as free acids and ketenes. Product ion spectra of [PC-CH3]? suggest favorable cleavage at the sn-2 position over the sn-1 due to distinct differences in the relative abundances. In contrast, collisional activation of PC cations is absent of abundant fatty acid chain-related product ions and typically indicates only the lipid class via formation of the phosphocholine cation. A solution phase method to produce the gas-phase adducted PC anion is also demonstrated. Product ion spectra derived from the solution phase method are similar to the results generated via ion/ion chemistry. This work demonstrates a gas-phase means to increase structural characterization of phosphatidylcholines via ion/ion chemistry. PMID:23469867

Stutzman, John R.; Blanksby, Stephen J.; McLuckey, Scott A.

2013-01-01

388

Gas-Phase Oxidation, Particle Uptake, and Product Studies of Isoprene Epoxydiols  

NASA Astrophysics Data System (ADS)

Isoprene epoxydiols (IEPOX), discovered in 2009 as low-NOx atmospheric oxidation products of the ubiquitous biogenic precursor isoprene, are key intermediates in the formation of secondary organic aerosol (SOA) from biogenic emissions. Recent studies carried out in the Caltech environmental chambers have elucidated the gas-phase OH oxidation rates and products, particle uptake rates, and particle-phase OH oxidation products of three isomers of IEPOX synthesized in-house. Gas-phase oxidation studies were conducted in 1 m3 chambers at both high- and low-NOx conditions, and were monitored by GC-FID, two types of chemical ionization mass spectrometry (CIMS), and GC-CIMS. Comparisons with previous studies on isoprene showed that the two ?-IEPOX isomers dominate over the ? isomers under atmospheric conditions, and the use of propene as an internal standard provided a robust estimate of OH oxidation rates between 0.99*10-11 and 1.67*10-11 cm3molec-1s-1 for the three isomers. Particle uptake and oxidation studies were conducted in 28 m3 chambers, and were monitored by GC-FID, CIMS, an aerosol mass spectrometer (AMS), and a differential mobility analyzer (DMA). Particle uptake showed a strong dependence on humidity, with no uptake on dry seed, and was faster on ammonium sulfate seed than sodium chloride seed. Particle-phase oxidation gave similar products to gas-phase oxidation by OH radicals.

Bates, K. H.; Nguyen, T. B.; St Clair, J. M.; Crounse, J.; Zhang, X.; Coggon, M.; Schwantes, R.; Bennett, N.; Stoltz, B.; Wennberg, P. O.; Seinfeld, J.

2013-12-01

389

Molecular Dynamics Modeling of Hypersonic Gas-Phase and Gas-Surface Reactions  

NASA Astrophysics Data System (ADS)

Efforts to use molecular dynamics (MD) to develop both non-equilibrium dissociation models required in the shock layer as well as gas-surface interaction models specifically for surface catalysis will be summarized. First, an accelerated MD algorithm for dilute gases is presented, called the Event-Driven/Time-Driven (ED/TD) MD method. The method detects and moves molecules directly to their impending collision while still integrating each collision, including multi-body collisions, using conventional Time-Driven (TD) MD with an arbitrary inter-atomic potential. The simulation thus proceeds at time steps approaching the mean-collision-time. Preliminary nonequilibrium relaxation and normal shock wave simulations are in excellent agreement with direct simulation Monte Carlo (DSMC) results with large speedups over conventional TD MD, especially at low densities. Second, an MD simulation technique to study surface catalysis employing the ReaxFF inter-atomic potential is detailed. SiO2 surfaces are equilibrated with a dissociated gas mixture at various temperatures and pressures, establishing surface coverage. Rates of dominant reaction mechanisms, including adsorption, desorption, and E-R/L-H recombination, are then determined by counting individual events. The experimentally measured exponential dependence of recombination coefficient on temperature is well predicted by the MD simulations.

Schwartzentruber, T. E.; Norman, P.; Valentini, P.

2011-05-01

390

Nucleation and growth of /sup 3/He-B in /sup 3/He-A  

SciTech Connect

The /sup 3/He A ..-->.. B transition is remarkable for a number of reasons. Because of the small bulk free energy difference between the two phases, the probability of homogeneous thermal nucleation of the B phase is vanishingly small. Thus the experimental fact that the B phase nucleates readily from the A phase is not understood. The A ..-->.. B transition is also remarkable in that when it occurs after cooling from above the critical temperature, it occurs in an extreme state of supercooling known as hypercooling. In this situation, the velocity of propagation of the A-B phase interface is controlled by microscopic phenomena rather than by thermal diffusion. We briefly review our recent work on both these topics, including the velocity of propagation of the A-B interface through hypercooled /sup 3/He-A, a search for cosmic-ray-induced B-phase nucleation, and preliminary observations of B-phase nucleation locations and temperatures. 15 refs.

Swift, G.W.; Buchanan, D.S.

1987-01-01

391

Rapid granular flows on a rough incline: phase diagram, gas transition, and effects of air drag  

E-print Network

We report experiments on the overall phase diagram of granular flows on an incline with emphasis on high inclination angles where the mean layer velocity approaches the terminal velocity of a single particle free falling in air. The granular flow was characterized by measurements of the surface velocity, the average layer height, and the mean density of the layer as functions of the hopper opening, the plane inclination angle and the downstream distance x of the flow. At high inclination angles the flow does not reach an x-invariant steady state over the length of the inclined plane. For low volume flow rates, a transition was detected between dense and very dilute (gas) flow regimes. We show using a vacuum flow channel that air did not qualitatively change the phase diagram and did not quantitatively modify mean flow velocities of the granular layer except for small changes in the very dilute gas-like phase.

Tamas Borzsonyi; Robert E. Ecke

2006-11-16

392

Inhibited phase behavior of gas hydrates in graphene oxide: influences of surface and geometric constraints.  

PubMed

Porous materials have provided us unprecedented opportunities to develop emerging technologies such as molecular storage systems and separation mechanisms. Pores have also been used as supports to contain gas hydrates for the application in gas treatments. Necessarily, an exact understanding of the properties of gas hydrates in confining pores is important. Here, we investigated the formation of CO2, CH4 and N2 hydrates in non-interlamellar voids in graphene oxide (GO), and their thermodynamic behaviors. For that, low temperature XRD and P-T traces were conducted to analyze the water structure and confirm hydrate formation, respectively, in GO after its exposure to gaseous molecules. Confinement and strong interaction of water with the hydrophilic surface of graphene oxide reduce water activity, which leads to the inhibited phase behavior of gas hydrates. PMID:25232710

Kim, Daeok; Kim, Dae Woo; Lim, Hyung-Kyu; Jeon, Jiwon; Kim, Hyungjun; Jung, Hee-Tae; Lee, Huen

2014-11-01

393

Use of ionic liquids as stationary phases in hyphenated gas chromatography techniques.  

PubMed

In the past decades a consistent number of ionic liquids have been specifically synthesized and evaluated as stationary phase in gas chromatography. Ionic liquid, also defined as "molten salts", are a class of organic non-molecular solvents liquid at room temperature (RTILs) that satisfy most of the requirements of a GC stationary phase, among which a high viscosity, the possibility to tune the selectivity (by changing the cation-anion combination) and a high thermal stability. The choice of the proper stationary phase plays a key role in the improvement/optimization of a GC method, and although the use of IL as stationary phases is still not well-established, the general interest in their applications has greatly increased, thanks to their particular properties. The present contribution provides an overview on recent evaluations and applications of IL stationary phases, focusing in particular on the use of these novel tools in hyphenated GC-based techniques. PMID:22621883

Ragonese, Carla; Sciarrone, Danilo; Tranchida, Peter Quinto; Dugo, Paola; Mondello, Luigi

2012-09-14

394

Fluid Phase Separation (FPS) experiment for flight on a space shuttle Get Away Special (GAS) canister  

NASA Technical Reports Server (NTRS)

The separation of fluid phases in microgravity environments is of importance to environmental control and life support systems (ECLSS) and materials processing in space. A successful fluid phase separation experiment will demonstrate a proof of concept for the separation technique and add to the knowledge base of material behavior. The phase separation experiment will contain a premixed fluid which will be exposed to a microgravity environment. After the phase separation of the compound has occurred, small samples of each of the species will be taken for analysis on the Earth. By correlating the time of separation and the temperature history of the fluid, it will be possible to characterize the process. The experiment has been integrated into space available on a manifested Get Away Special (GAS) experiment, CONCAP 2, part of the Consortium for Materials Complex Autonomous Payload (CAP) Program, scheduled for STS-42. The design and the production of a fluid phase separation experiment for rapid implementation at low cost is presented.

Peters, Bruce; Wingo, Dennis; Bower, Mark; Amborski, Robert; Blount, Laura; Daniel, Alan; Hagood, Bob; Handley, James; Hediger, Donald; Jimmerson, Lisa

1990-01-01

395

Nucleation in Submonolayer Electrodeposition  

NASA Astrophysics Data System (ADS)

We have studied phin situ the ordering of a two-dimensional CuCl crystal electrodeposited on a Pt(111) surface. We simultaneously measured high-resolution time-resolved x-ray scattering and chronoamperometric transients. Both measurements were synchronized with the leading edge of an applied potential step which stimulated the desorption of Cu and subsequent ordering of the CuCl crystal. In all cases, the current transient occurs on a shorter time-scale than the development of crystalline order. The scattered x-ray intensity data (2 × 10^4 data points) vs. time and transverse momentum transfer can be fit to an Avrami-like function with only three parameters. By performing a series of voltage-step experiments, we demonstrate that the ordering time diverges with applied potential ? as ? ~ exp [ 1 / (? - ?_0) ], consistent with the nucleation and growth of two-dimensional clusters. Monitoring the time-dependent widths of the x-ray peak, we see a narrowing corresponding to the growing clusters. Further information is available at http://www.msc.cornell.edu/ adam

Finnefrock, A. C.; Ringland, K. L.; Abruña, H. D.; Brock, J. D.

1998-03-01

396

LSPRAY: Lagrangian Spray Solver for Applications With Parallel Computing and Unstructured Gas-Phase Flow Solvers  

NASA Technical Reports Server (NTRS)

Sprays occur in a wide variety of industrial and power applications and in the processing of materials. A liquid spray is a phase flow with a gas as the continuous phase and a liquid as the dispersed phase (in the form of droplets or ligaments). Interactions between the two phases, which are coupled through exchanges of mass, momentum, and energy, can occur in different ways at different times and locations involving various thermal, mass, and fluid dynamic factors. An understanding of the flow, combustion, and thermal properties of a rapidly vaporizing spray requires careful modeling of the rate-controlling processes associated with the spray's turbulent transport, mixing, chemical kinetics, evaporation, and spreading rates, as well as other phenomena. In an attempt to advance the state-of-the-art in multidimensional numerical methods, we at the NASA Lewis Research Center extended our previous work on sprays to unstructured grids and parallel computing. LSPRAY, which was developed by M.S. Raju of Nyma, Inc., is designed to be massively parallel and could easily be coupled with any existing gas-phase flow and/or Monte Carlo probability density function (PDF) solver. The LSPRAY solver accommodates the use of an unstructured mesh with mixed triangular, quadrilateral, and/or tetrahedral elements in the gas-phase solvers. It is used specifically for fuel sprays within gas turbine combustors, but it has many other uses. The spray model used in LSPRAY provided favorable results when applied to stratified-charge rotary combustion (Wankel) engines and several other confined and unconfined spray flames. The source code will be available with the National Combustion Code (NCC) as a complete package.

Raju, Manthena S.

1998-01-01

397

FIELD METHODS TO MEASURE CONTAMINANT REMOVAL EFFECTIVENESS OF GAS-PHASE AIR FILTRATION EQUIPMENT - PHASE 1: SEARCH OF LITERATURE AND PRIOR ART  

EPA Science Inventory

The report, Phase 1 of a two-phase research project, gives results of a literature search into the effectiveness of in-field gas-phase air filtration equipment (GPAFE) test methods, including required instrumentation and costs. GPAFE has been used in heating, ventilation, and ...

398

Monitoring CO2 gas-phase injection in a shallow sand aquifer using cross borehole GPR  

NASA Astrophysics Data System (ADS)

An important issue that needs attention in designing effective storage schemes for CO2 storage in deep geologic formations is risk assessment of potential leakage. Leaking gas may threat surface and groundwater sources as well as vegetation. We have designed an experiment where we were track the movement of an injected CO2 gas-phase in an unconfined aquifer using cross borehole GPR. The test site is located in the south-western part of Denmark. The aquifer at the site consists of fine to coarse glacial melt water sands, which are staggered in slightly tilted layers. In all experiments gas was injected for 48 hours with flow rates between 9-16 g/min. The screen of the injection well is 10 m below ground level or 8 m below the water table. Initially an array of four GPR boreholes was installed around the injection well and subsequently two extra GPR Boreholes were installed downwards of dominating gas flow direction. GPR-data were acquired in zero offset (1D) and multiple offset (2D) configurations prior and during the injection. To support the GPR measurements 12 Decagon 5-TE soil moisture probes were installed at various dept for the last experiments. Both set of GPR data showed that a plume developed at the depth of the injection screen and that the injected gas primarily spread towards South-East. The geology consists of slightly tilting layers, which may cause migration of the gas plume along the interface of the coarse and fine sand and out of the monitoring area. The results confirmed the notion that geological heterogeneity has a critical impact on the gas migration pattern. The gas plume migration was further analysed by the multi-phase numerical code T2VOC a part of the TOUGH family.

Lassen, R. N.; Looms, M. C.; Jensen, K. H.; Sonnenborg, T.

2012-12-01

399

From the gas phase to aqueous solution: Vibrational spectroscopy, Raman optical activity and conformational structure of carbohydrates  

Microsoft Academic Search

Structural investigations of isolated and hydrated glucose, galactose and lactose structures in the gas phase based upon infra-red ion dip (IRID) spectroscopy conducted at low temperatures, are linked with parallel investigations conducted in aqueous solution at 298K based upon measurements of their vibrational Raman and Raman optical activity (ROA) spectra. ‘Basis sets’ of computed (gas phase) Raman and ROA spectra

Neil A. Macleod; Christian Johannessen; Lutz Hecht; Laurence D. Barron; John P. Simons

2006-01-01

400

Outer Co(II) ions in Co-ZIF-67 reversibly adsorb oxygen from both gas phase and liquid water.  

PubMed

Outer Co(II) species in Co-ZIF-67 coordinate molecular oxygen both from the gas phase and liquid water, through an adsorption process (presumably yielding in both cases surface superoxo species), respectively weak and reversible (gas phase), and strong and irreversible (liquid); in the latter case desorption is however brought about by illumination with solar light comprising the UV component. PMID:24562186

Saracco, Guido; Vankova, Svetoslava; Pagliano, Cristina; Bonelli, Barbara; Garrone, Edoardo

2014-04-01

401

Climate Impacts of Ice Nucleation  

SciTech Connect

Several different ice nucleation parameterizations in two different General Circulation Models are used to understand the effects of ice nucleation on the mean climate state, and the climate effect of aerosol perturbations to ice clouds. The simulations have different ice microphysical states that are consistent with the spread of observations. These different states occur from different parameterizations of the ice cloud nucleation processes, and feature different balances of homogeneous and heterogeneous nucleation. At reasonable efficiencies, consistent with laboratory measurements and constrained by the global radiative balance, black carbon has a small (-0.06 Wm?2) and not statistically significant climate effect. Indirect effects of anthropogenic aerosols on cirrus clouds occur mostly due to increases in homogeneous nucleation fraction as a consequence of anthropogenic sulfur emissions. The resulting ice indirect effects do not seem strongly dependent on the ice micro-physical balance, but are slightly larger for those states with less homogeneous nucleation in the base state. The total ice AIE is estimated at 0.26±0.09 Wm?2 (1? uncertainty). This represents an offset of 20-30% of the simulated total Aerosol Indirect Effect for ice and liquid clouds.

Gettelman, A.; Liu, Xiaohong; Barahona, Donifan; Lohmann, U.; Chen, Chih-Chieh

2012-10-19

402

Design and Development of Gas-Liquid Cylindrical Cyclone Compact Separators for Three-Phase Flow  

SciTech Connect

The objective of this five-year project (October 1997--September 2002) was to expand the current research activities of Tulsa University Separation Technology Projects (TUSTP) to multiphase oil/water/gas separation. This project was executed in two phases. Phase I (1997--2000) focused on the investigations of the complex multiphase hydrodynamic flow behavior in a three-phase Gas-Liquid Cylindrical Cyclone (GLCC) Separator. The activities of this phase included the development of a mechanistic model, a computational fluid dynamics (CFD) simulator, and detailed experimentation on the three-phase GLCC. The experimental and CFD simulation results will be suitably integrated with the mechanistic model. In Phase II (2000--2002), the developed GLCC separator will be tested under high pressure and real crude conditions. This is crucial for validating the GLCC design for field application and facilitating easy and rapid technology deployment. Design criteria for industrial applications will be developed based on these results and will be incorporated into the mechanistic model by TUSTP.

Mohan, R.S.; Shoham, O.

2001-01-10

403

DYNAMIC MODELING STRATEGY FOR FLOW REGIME TRANSITION IN GAS-LIQUID TWO-PHASE FLOWS  

SciTech Connect

In modeling gas-liquid two-phase flows, the concept of flow regime has been used to characterize the global interfacial structure of the flows. Nearly all constitutive relations that provide closures to the interfacial transfers in two-phase flow models, such as the two-fluid model, are often flow regime dependent. Currently, the determination of the flow regimes is primarily based on flow regime maps or transition criteria, which are developed for steady-state, fully-developed flows and widely applied in nuclear reactor system safety analysis codes, such as RELAP5. As two-phase flows are observed to be dynamic in nature (fully-developed two-phase flows generally do not exist in real applications), it is of importance to model the flow regime transition dynamically for more accurate predictions of two-phase flows. The present work aims to develop a dynamic modeling strategy for determining flow regimes in gas-liquid two-phase flows through the introduction of interfacial area transport equations (IATEs) within the framework of a two-fluid model. The IATE is a transport equation that models the interfacial area concentration by considering the creation and destruction of the interfacial area, such as the fluid particle (bubble or liquid droplet) disintegration, boiling and evaporation; and fluid particle coalescence and condensation, respectively. For the flow regimes beyond bubbly flows, a two-group IATE has been proposed, in which bubbles are divided into two groups based on their size and shape (which are correlated), namely small bubbles and large bubbles. A preliminary approach to dynamically identifying the flow regimes is provided, in which discriminators are based on the predicted information, such as the void fraction and interfacial area concentration of small bubble and large bubble groups. This method is expected to be applied to computer codes to improve their predictive capabilities of gas-liquid two-phase flows, in particular for the applications in which flow regime transition occurs.

X. Wang; X. Sun; H. Zhao

2011-09-01

404

Influence of carrier and doping gases on silicon quantum dots nucleation  

NASA Astrophysics Data System (ADS)

We present a study of the influence of H 2 as a carrier gas on the nucleation and growth of silicon quantum dots (Si-QDs) on SiO 2 by chemical vapor deposition (CVD). Compared to deposition from pure SiH 4, the dilution of SiH 4 in H 2 leads to a strong decrease of the nucleation/growth rate, with the same Si-QDs morphology however. The effects of doping gas, phosphine and diborane, on Si-QDs nucleation and growth were also investigated. Silanol groups at the SiO 2 surface were identified as nucleation sites for Si-QDs. We study the influence of H 2 and doping gases on their activity toward Si-QDs nucleation.

Mazen, F.; Baron, T.; Hartmann, J. M.; Brémond, G.; Séméria, M. N.

2003-08-01

405

Transport of Gas Phase Radionuclides in a Fractured, Low-Permeability Reservoir  

NASA Astrophysics Data System (ADS)

The U.S. Atomic Energy Commission (predecessor to the Department of Energy, DOE) oversaw a joint program between industry and government in the 1960s and 1970s to develop technology to enhance production from low-permeability gas reservoirs using nuclear stimulation rather than conventional means (e.g., hydraulic and/or acid fracturing). Project Rio Blanco, located in the Piceance Basin, Colorado, was the third experiment under the program. Three 30-kiloton nuclear explosives were placed in a 2134 m deep well at 1780, 1899, and 2039 m below the land surface and detonated in May 1973. Although the reservoir was extensively fractured, complications such as radionuclide contamination of the gas prevented production and subsequent development of the technology. Two-dimensional numerical simulations were conducted to identify the main transport processes that have occurred and are currently occurring in relation to the detonations, and to estimate the extent of contamination in the reservoir. Minor modifications were made to TOUGH2, the multiphase, multicomponent reservoir simulator developed at Lawrence Berkeley National Laboratories. The simulator allows the explicit incorporation of fractures, as well as heat transport, phase change, and first order radionuclide decay. For a fractured two-phase (liquid and gas) reservoir, the largest velocities are of gases through the fractures. In the gas phase, tritium and one isotope of krypton are the principle radionuclides of concern. However, in addition to existing as a fast pathway, fractures also permit matrix diffusion as a retardation mechanism. Another retardation mechanism is radionuclide decay. Simulations show that incorporation of fractures can significantly alter transport rates, and that radionuclides in the gas phase can preferentially migrate upward due to the downward gravity drainage of liquid water in the pores. This project was funded by the National Nuclear Security Administration, Nevada Operations Office, under DOE Contract no. DE-AC08-00NV13609.

Cooper, C. A.; Chapman, J.

2001-12-01

406

Missing gas-phase source of HONO inferred from Zeppelin measurements in the troposphere  

NASA Astrophysics Data System (ADS)

Nitrous acid (HONO) is an important trace gas in the atmosphere due to its contribution to the cycles of nitrogen oxides (NOX) and hydrogen oxides (HOX). In the past decades, ground-based observations of HONO around the world showed much higher daytime concentrations than can be explained by the known gas-phase chemistry (i.e., HONO + h? ? OH + NO, HONO + OH ? NO2 + H2O, OH + NO + M ? HONO + M). Different light-dependent reactions on ground surfaces have been proposed as additional daytime HONO sources. However, due to lack of measurements, little is known about the concentrations of HONO and its sources in the planetary boundary layer (PBL) at higher altitudes above the earth's surface. The airship Zeppelin NT is an ideal platform to investigate the chemistry and dynamics of the PBL. During the PEGASOS field campaigns in 2012 and 2013, HONO and its gas-phase sources and sinks were measured simultaneously on-board the airship Zeppelin NT, for the lowest 1 km of the PBL. In the upper part of the altitude range during morning hours, when the airmass is still isolated from processes at the earth's surface by the remaining nocturnal boundary layer, we find unexpectedly large concentrations of HONO which can neither be explained by heterogeneous reactions on aerosol and ground surfaces, nor by known gas-phase reactions. Our observations show evidence for an unknown gas-phase light-dependent HONO production which dominates the overall HONO formation in the lower troposphere. This new HONO source requires NOX and possibly OH or HO2 radicals. As a result, the general impact of HONO on the OH formation is likely overestimated.

Li, Xin; Rohrer, Franz; Hofzumahaus, Andreas; Brauers, Theo; Häseler, Rolf; Bohn, Birger; Broch, Sebastian; Fuchs, Hendrik; Gomm, Sebastian; Holland, Frank; Jäger, Julia; Kaiser, Jennifer; Keutsch, Frank N.; Lohse, Insa; Tillmann, Ralf; Wegener, Robert; Wolfe, Glenn M.; Mentel, Thomas F.; Kiendler-Scharr, Astrid; Wahner, Andreas

2014-05-01

407

Absorbance characteristics of a liquid-phase gas sensor based on gas-permeable liquid core waveguides.  

PubMed

The absorbance characteristics and influential factors on these characteristics for a liquid-phase gas sensor, which is based on gas-permeable liquid core waveguides (LCWs), are studied from theoretical and experimental viewpoints in this paper. According to theory, it is predicted that absorbance is proportional to the analyte concentration, sampling time, analyte diffusion coefficient, and geometric factor of this device when the depletion layer of the analyte is ignored. The experimental results are in agreement with the theoretical hypothesis. According to the experimental results, absorbance is time-dependent and increasing linearly over time after the requisite response time with a linear correlation coefficient r(2)>0.999. In the linear region, the rate of absorbance change (RAC) indicates improved linearity with sample concentration and a relative higher sensitivity than instantaneous absorbance does. By using a core liquid that is more affinitive to the analyte, reducing wall thickness and the inner diameter of the tubing, or increasing sample flow rate limitedly, the response time can be decreased and the sensitivity can be increased. However, increasing the LCW length can only enhance sensitivity and has no effect on response time. For liquid phase detection, there is a maximum flow rate, and the absorbance will decrease beyond the stated limit. Under experimental conditions, hexane as the LCW core solvent, a tubing wall thickness of 0.1 mm, a length of 10 cm, and a flow rate of 12 mL min(-1), the detection results for the aqueous benzene sample demonstrate a response time of 4 min. Additionally, the standard curve for the RAC versus concentration is RAC=0.0267c+0.0351 (AU min(-1)), with r(2)=0.9922 within concentrations of 0.5-3.0 mg L(-1). The relative error for 0.5 mg L(-1) benzene (n=6) is 7.4±3.7%, and the LOD is 0.04 mg L(-1). This research can provide theoretical and practical guides for liquid-phase gas sensor design and development based on a gas-permeable Teflon AF 2400 LCW. PMID:24267083

Peng, Pei; Wang, Wei; Zhang, Li; Su, Shiguang; Wang, Jiahui

2013-12-01

408

Sound Propagation in an inhomogeneous two-phase system: the influence of the gas bubble concentration on the sound source model.  

NASA Astrophysics Data System (ADS)

Volcanic explosions produce pressure perturbations in the atmosphere (infrasound) which are not contaminated by path effects as for the seismic wavefield and contain useful and direct informations on the source dynamics. Recently, many dynamical models of the explosive process are based on the analysis of the acoustic field. We have analyzed the acoustic wave field in terms of elastic wave propagation in a two-phase medium where the viscosity and compressibility are spatially inhomogeneous. At low pressure (<10 MPa) the magma can not be considered as an homogeneous medium, but has to be treated as a mixture of fluid magma and gas bubbles. Gas bubble nucleation starts when the pressure of the system drops below the supersaturation level (a few hundreds of meters for H2O in basaltic magmas) and increases towards the surface, reaching its maximum value at the magma-air interface. Such a variation is non-linear with depth and is particularly strong at shallow depth. With the decrease of depth the density of the mixture and the sound velocity drop drastically while the shear viscosity of the mixture increases. We calculated the propagation of an elastic wavefield generated by an explosive source embedded in the magma column as function of the void fraction increase in the magma. Large gas bubble concentrations (>70%) prevent the elastic wavefield to propagate suggesting that or the source is shallow or it is characterized by a high pressure drop. We propose a source model which explain the infrasonic wavefield in terms of a shallow unsteady pressure front.

Marchetti, E.; Ichihara, M.; Ripepe, M.

2001-12-01

409

Gas phase chemical studies of superheavy elements using the Dubna gas-filled recoil separator - Stopping range determination  

NASA Astrophysics Data System (ADS)

Currently, gas phase chemistry experiments with heaviest elements are usually performed with the gas-jet technique with the disadvantage that all reaction products are collected in a gas-filled thermalisation chamber adjacent to the target. The incorporation of a physical preseparation device between target and collection chamber opens up the perspective to perform new chemical studies. But this approach requires detailed knowledge of the stopping force (STF) of the heaviest elements in various materials. Measurements of the energy loss of mercury (Hg), radon (Rn), and nobelium (No) in Mylar and argon (Ar) were performed at low kinetic energies of around (40-270) keV per nucleon. The experimentally obtained values were compared with STF calculations of the commonly used program for calculating stopping and ranges of ions in matter (SRIM). Using the obtained data points an extrapolation of the STF up to element 114, eka-lead, in the same stopping media was carried out. These estimations were applied to design and to perform a first chemical experiment with a superheavy element behind a physical preseparator using the nuclear fusion reaction 244Pu( 48Ca; 3n) 289114. One decay chain assigned to an atom of 285112, the ?-decay product of 289114, was observed.

Wittwer, D.; Abdullin, F. Sh.; Aksenov, N. V.; Albin, Yu. V.; Bozhikov, G. A.; Dmitriev, S. N.; Dressler, R.; Eichler, R.; Gäggeler, H. W.; Henderson, R. A.; Hübener, S.; Kenneally, J. M.; Lebedev, V. Ya.; Lobanov, Yu. V.; Moody, K. J.; Oganessian, Yu. Ts.; Petrushkin, O. V.; Polyakov, A. N.; Piguet, D.; Rasmussen, P.; Sagaidak, R. N.; Serov, A.; Shirokovsky, I. V.; Shaughnessy, D. A.; Shishkin, S. V.; Sukhov, A. M.; Stoyer, M. A.; Stoyer, N. J.; Tereshatov, E. E.; Tsyganov, Yu. S.; Utyonkov, V. K.; Vostokin, G. K.; Wegrzecki, M.; Wilk, P. A.

2010-01-01

410

DFT study on foscarnet as an antiviral drug: Conformer analysis, gas phase acidity, metal ion affinity and influence of metal complexation on gas phase acidity  

NASA Astrophysics Data System (ADS)

This work presents a density functional theory study of Foscarnet (FOS), an anti-viral drug. In this study conformational analysis, gas phase acidity and metal ion affinity (MIA) of foscarnet with selected cations from alkalis (Li+, Na+, and K+) and alkaline earths (Ca2+ and Mg2+) were calculated. All of the structure optimizations and frequency calculations were performed at the B3LYP level of theory with 6-311++G(d,p) basis set. The calculations showed the MIA order to be K+ < Na+ < Li+ < Ca2+ < Mg2+, in agreement with increasing gas phase acidity of the foscarnet molecule during complexation. Natural bond orbital theory (NBO) and quantum theory of atoms in molecules (QTAIM) were used to investigate the charge transfer process and the nature of interactions in the formed complexes. The results of the NBO analysis revealed that Mn+ acts as charge acceptor and the amount of charge transfer is in agreement with MIA. The QTAIM analysis shows that (Msbnd O) coordinations are electrostatic in nature, and their strengths are in agreement with electron densities at their bond critical points (BCP).

Khalili, Behzad; Rimaz, Mehdi; Tondro, Tahereh

2015-01-01

411

Experimental Study of Gas-Liquid Two-Phase Flow in Glass Micromodels  

NASA Astrophysics Data System (ADS)

To estimate the most important flow variables in reservoir engineering, such as the relative permeability, it is required to know with high precision, other variables such as saturation, pressure drop of each phase, and porous media data such as porosity and absolute permeability. In this study, experimental tests were performed inside a glass micromodel using gas-liquid two-phase flow in steady-state conditions. The liquid-phase flow and the pressure drop of the porous media were determined. Additionally, the flow development inside the porous media was visualized using a high-speed video camera system. These pictures were recorded at 500 fps, and they were used to compute the phase saturation and the gas velocity in the glass micromodel. The visualization was performed in three regions of the glass micromodel demonstrating that saturation gradients were not present. The effect of the capillary number was studied over the gas-liquid relative permeability curves and on the flow mechanisms. It was concluded that high flow rates minimize edge effects, that the capillary number modifies the relative permeability values and the flow patterns inside the micromodel, and that the high-speed visualization is an efficient and accurate technique to determine saturation values and to study the flow patterns in transparent porous media such as glass micromodels.

Gutiérrez, B.; Juarez, F.; Ornelas, L.; Zeppieri, S.; de Ramos, A. López

2008-12-01

412

Attainment of unstable ? nucleation of glycine through novel swift cooling crystallization process  

NASA Astrophysics Data System (ADS)

The sudden cooling of mother liquor from high temperature to a temperature below the ambient through the recently introduced swift cooling crystallization process yielded the ? nucleation of glycine even in the absence of anti-solvents and additives. Experiments were continued at different supersaturation and stirring levels. The nucleation matrix resulted out of these 135 experiments revealed that, even at lower supersaturation and lower stirring rates, the unstable ? nucleation could be achieved. This attained result contrasts the existing reports in which ? nucleation is achieved only at higher supersaturation levels. The intermediate supersaturation and stirring levels facilitate both the ? and ? nucleation through solution mediated phase transformation while the higher supersaturation and stirring levels facilitate only the ? nucleation of glycine in the system. The swift cooling method adopted declines the energy barrier that inherently exists for ? and enables its nucleation in the system. Analytically the nucleation parameters of ? and ? polymorphs were estimated based on Classical Nucleation Theory. Form of crystallization of the nucleated polymorphs of glycine was confirmed by powder x-ray diffraction analysis.

Renuka Devi, K.; Gnanakamatchi, V.; Srinivasan, K.

2014-08-01

413

Monolithically-integrated MicroChemLab for gas-phase chemical analysis.  

SciTech Connect

Sandia National Labs has developed an autonomous, hand-held system for sensitive/selective detection of gas-phase chemicals. Through the sequential connection of microfabricated preconcentrators (PC), gas chromatography columns (GC) and a surface acoustic wave (SAW) detector arrays, the MicroChemLab{trademark} system is capable of selective and sensitive chemical detection in real-world environments. To date, interconnection of these key components has primarily been achieved in a hybrid fashion on a circuit board modified to include fluidic connections. The monolithic integration of the PC and GC with a silicon-based acoustic detector is the subject of this work.

Kottenstette, Richard Joseph; Adkins, Douglas Ray; Manley, Robert George; Lewis, Patrick Raymond; Bauer, Joseph M.; Manginell, Ronald Paul; Okandan, Murat; Shul, Randy John; Sokolowski, Sara Suzette

2003-06-01

414

Many-body braiding phases in a rotating strongly correlated photon gas  

NASA Astrophysics Data System (ADS)

We present a theoretical study of fractional quantum Hall physics in a rotating gas of strongly interacting photons in a single cavity with a large optical nonlinearity. Photons are injected into the cavity by a Laguerre-Gauss laser beam with a non-zero orbital angular momentum. The Laughlin-like few-photon eigenstates appear as sharp resonances in the transmission spectra. Using additional localized repulsive potentials, quasi-holes can be created in the photon gas and then braided around in space: an unambiguous signature of the many-body Berry phase under exchange of two quasi-holes is observed as a spectral shift of the corresponding transmission resonance.

Umucal?lar, R. O.; Carusotto, I.

2013-11-01

415

MODELING AEROSOL FORMATION FROM ALPHA-PINENE + NOX IN THE PRESENCE OF NATURAL SUNLIGHT USING GAS PHASE KINETICS AND GAS-PARTICLE PARTITIONING THEORY. (R826771)  

EPA Science Inventory

A kinetic mechanism was used to link and model the gas-phase reactions and aerosol accumulation resulting from -pinene reactions in the presence of sunlight, ozone (O3), and oxides of nitrogen (NO ...

416

Gas-phase chemistry in dense interstellar clouds including grain surface molecular depletion and desorption  

NASA Technical Reports Server (NTRS)

We present time-dependent models of the chemical evolution of molecular clouds which include depletion of atoms and molecules onto grain surfaces and desorption, as well as gas-phase interactions. We have included three mechanisms to remove species from the grain mantles: thermal evaporation, cosmic-ray-induced heating, and photodesorption. A wide range of parameter space has been explored to examine the abundance of species present both on the grain mantles and in the gas phase as a function of both position in the cloud (visual extinction) and of evolutionary state (time). The dominant mechanism that removes molecules from the grain mantles is cosmic-ray desorption. At times greater than the depletion timescale, the abundances of some simple species agree with abundances observed in the cold dark cloud TMC-1. Even though cosmic-ray desorption preserves the gas-phase chemistry at late times, molecules do show significant depletions from the gas phase. Examination of the dependence of depletion as a function of density shows that when the density increases from 10(exp 3)/cc to 10(exp 5)/cc several species including HCO(+), HCN, and CN show gas-phase abundance reductions of over an order of magnitude. The CO: H2O ratio in the grain mantles for our standard model is on the order of 10:1, in reasonable agreement with observations of nonpolar CO ice features in rho Ophiuchus and Serpens. We have also examined the interdependence of CO depletion with the space density of molecular hydrogen and binding energy to the grain surface. We find that the observed depletion of CO in Taurus in inconsistent with CO bonding in an H2O rich mantle, in agreement with observations. We suggest that if interstellar grains consist of an outer layer of CO ice, then the binding energies for many species to the grain mantle may be lower than commonly used, and a significant portion of molecular material may be maintained in the gas phase.

Bergin, E. A.; Langer, W. D.; Goldsmith, P. F.

1995-01-01

417

Dynamic Nucleation of Ice Induced by a Single Stable Cavitation Bubble  

NASA Technical Reports Server (NTRS)

Dynamic nucleation of ice induced by caviation bubble in undercooled water is observed using an acoustic levitation technique. The observation indicates that a high pressure pulse associated with a collapsing bubble is indeed responsible for the nucleation of a high pressure phase of ice.

Ohsaka, Kenichi; Trinh, Eugene H.

1997-01-01

418

Abbreviated MOVPE nucleation of III-nitride light-emitting diodes on nano-patterned sapphire  

E-print Network

Abbreviated MOVPE nucleation of III-nitride light-emitting diodes on nano-patterned sapphire Yik t Metalorganic vapor phase epitaxy (MOVPE) nucleation studies of GaN on planar sapphire and nano- patterned AGOG (Deposition of Aluminum, Growth of Oxide, and Grain growth) sapphire substrates were conducted. The use

Gilchrist, James F.

419

Gas phase laser synthesis and processing of calcium phosphate nanoparticles for biomedical applications  

NASA Astrophysics Data System (ADS)

Biochemical processes make pervasive use of calcium and phosphate ions. Calcium phosphate salts that are naturally nontoxic and bioactive have been used for several medical applications in form of coatings and micropowders. Nanoparticle-based calcium phosphates have been shown to be internalized by living cells and be effective in DNA transfection, drug delivery, and transport of fluorophores for imaging of intracellular processes. They are also expected to interact strongly with cell adhesive proteins and are therefore promising elements in approaches to mimic the complex environment of the extra cellular matrix of bone. Harnessing this biomedical potential requires the ability to control the numerous characteristics of nanophase calcium phosphates that affect biological response, including nanoparticle chemical composition, crystal phase, crystallinity, crystallographic orientation of exposed faces, size, shape, surface area, number concentration, and degree of aggregation. This dissertation focuses on the use of laser-induced gas-phase synthesis for creation of calcium phosphate nanoparticles, and corresponding nanoparticle-based substrates that could offer new opportunities for guiding biological responses through well-controlled biochemical and topological cues. Gas-phase synthesis of nanoparticles has several characteristics that could enhance control over particle morphology, crystallinity, and surface area, compared to liquid-phase techniques. Synthesis from gas-phase precursors can be carried out at high temperatures and in high-purity inert or reactive gas backgrounds, enabling good control of chemistry, crystal structure, and purity. Moreover, the particle mean free path and number concentration can be controlled independently. This allows regulation of interparticle collision rates, which can be adjusted to limit aggregation. High-temperature synthesis of well-separated particles is therefore possible. In this work high power lasers are employed to vaporize microcrystalline calcium phosphate materials to generate an aerosol of nanoparticles which is further processed and deposited using principles of aerosol mechanics. Particles and resulting particle-based systems are analyzed by transmission electron microscopy, atomic force microscopy, X-ray diffraction, and optical absorption. Obtained substrates are functionalized with cell adhesive peptides. Findings show that laser-induced gas-phase synthesis provides attractive new dimensions in the controlled fabrication of calcium phosphate nanoparticles, including manipulation not only of size and chemical composition, but also crystal phase make-up, fractal structure, and nanotopography of derived substrates.

Bapat, Parimal V.

420

Identification of gas\\/liquid two-phase flow regime through ERT-based measurement and feature extraction  

Microsoft Academic Search

Gas\\/liquid two-phase flow is of great importance in various industrial processes. As the most important characteristic of a two-phase flow, the flow regime not only characterizes the flow condition in an explicit way, but also determines the measurement model in each measuring method. Based on the application of Electrical Resistance Tomography (ERT) to a gas\\/liquid two-phase flow on a vertical

Chao Tan; Feng Dong; Mengmeng Wu

2007-01-01

421

A Chain of Modeling Tools For Gas and Aqueous Phase Chemstry  

NASA Astrophysics Data System (ADS)

Atmospheric chemistry is characterized by the use of large set of chemical species and reactions. Handling with the set of data required for the definition of the model is a quite difficult task. We prsent in this short article a preprocessor for diphasic models (gas phase and aqueous phase in cloud droplets) named SPACK. The main interest of SPACK is the automatic generation of lumped species related to fast equilibria. We also developped a linear tangent model using the automatic differentiation tool named ODYSSEE in order to perform a sensitivity analysis of an atmospheric multi- phase mechanism based on RADM2 kinetic scheme.Local sensitivity coefficients are computed for two different scenarii. We focus in this study on the sensitivity of the ozone,NOx,HOx, system with respect to some aqueous phase reactions and we inves- tigate the influence of the reduction in the photolysis rates in the area below the cloud region.

Audiffren, N.; Djouad, R.; Sportisse, B.

422

Beyond phthalates: gas phase concentrations and modeled gas/particle distribution of modern plasticizers.  

PubMed

The ongoing health debate about polymer plasticizers based on the esters of phthalic acid, especially di(2-ethylhexyl) phthalate (DEHP), has caused a trend towards using phthalates of lower volatility such as diisononyl phthalate (DINP) and towards other acid esters, such as adipates, terephthalates, citrates, etc. Probably the most important of these so-called "alternative" plasticizers is diisononyl cyclohexane-1,2-dicarboxylate (DINCH). In the indoor environment, the continuously growing market share of this compound since its launch in 2002 is inter alia apparent from the increasing concentration of DINCH in settled house dust. From the epidemiological point of view there is considerable interest in identifying how semi-volatile organic compounds (SVOCs) distribute in the indoor environment, especially in air, airborne particles and sedimented house dust. This, however, requires reliable experimental concentration data for the different media and good measurements or estimates of their physical and chemical properties. This paper reports on air concentrations for DINP, DINCH, diisobutyl phthalate (DIBP), diisobutyl adipate (DIBA), diisobutyl succinate (DIBS) and diisobutyl glutarate (DIBG) from emission studies in the Field and Laboratory Emission Cell (FLEC). For DINP and DINCH it took about 50 days to reach the steady-state value: for four months no decay in the concentration could be observed. Moreover, vapor pressures p(0) and octanol-air partitioning coefficients K(OA) were obtained for 37 phthalate and non-phthalate plasticizers from two different algorithms: EPI Suite and SPARC. It is shown that calculated gas/particle partition coefficients K(p) and fractions can widely differ due to the uncertainty in the predicted p(0) and K(OA) values. For most of the investigated compounds reliable experimental vapor pressures are not available. Rough estimates can be obtained from the measured emission rate of the pure compound in a microchamber as is shown for di-n-butyl phthalate (DnBP), di(2-ethylhexyl) adipate(DEHA), tri(octyl) trimellitate (TOTM) and DEHP. PMID:21764421

Schossler, Patrícia; Schripp, Tobias; Salthammer, Tunga; Bahadir, Müfit

2011-09-01

423

Heterogeneous ice nucleation on simulated secondary organic aerosol.  

PubMed

In this study, we have explored the phase behavior and the ice nucleation properties of secondary organic aerosol made from aqueous processing (aqSOA). AqSOA was made from the dark reactions of methylglyoxal with methylamine in simulated evaporated cloud droplets. The resulting particles were probed from 215 to 250 K using Raman spectroscopy coupled to an environmental cell. We find these particles are in a semisolid or glassy state based upon their behavior when exposed to mechanical pressure as well as their flow behavior. Further, we find that these aqSOA particles are poor depositional ice nuclei, in contrast to previous studies on simple mixtures of glassy organics. Additionally, we have studied the effect of ammonium sulfate on the phase, morphology, and ice nucleation behavior of the aqSOA. We find that the plasticizing effect of ammonium sulfate lowers the viscosity of the aqSOA, allowing the ammonium sulfate to effloresce within the aqSOA matrix. Upon humidification, the aqSOA matrix liquefies before it can depositionally nucleate ice, and the effloresced ammonium sulfate can act as an immersion mode ice nucleus. This change in the mode of nucleation is accompanied by an increase in the overall ice nucleation efficiency of the aqSOA particles. PMID:24410444

Schill, Gregory P; De Haan, David O; Tolbert, Margaret A

2014-02-01

424

Free gas in the regional hydrate stability zone: Implications for hydrate distribution and fracturing behavior  

Microsoft Academic Search

We show that hydrate distribution and fracture genesis in the hydrate stability zone are largely governed by the phase of methane supply. In systems where methane is supplied primarily as free gas, hydrate saturation increases upwards in the hydrate stability zone, and fractures nucleate in the middle of the stability zone where hydrate saturation is highest. In systems where methane

H. Daigle; B. Dugan

2010-01-01

425

Dynamical phases in quenched spin-orbit-coupled degenerate Fermi gas.  

PubMed

The spin-orbit-coupled degenerate Fermi gas provides a new platform for realizing topological superfluids and related topological excitations. However, previous studies have been mainly focused on the topological properties of the stationary ground state. Here, we investigate the quench dynamics of a spin-orbit-coupled two-dimensional Fermi gas in which the Zeeman field serves as the major quench parameter. Three post-quench dynamical phases are identified according to the asymptotic behaviour of the order parameter. In the undamped phase, a persistent oscillation of the order parameter may support a topological Floquet state with multiple edge states. In the damped phase, the magnitude of the order parameter approaches a constant via a power-law decay, which may support a dynamical topological phase with one edge state at the boundary. In the overdamped phase, the order parameter decays to zero exponentially although the condensate fraction remains finite. These predictions can be observed in the strong-coupling regime. PMID:25600665

Dong, Ying; Dong, Lin; Gong, Ming; Pu, Han

2015-01-01

426

Fluorometric method for the determination of gas-phase hydrogen peroxide  

NASA Technical Reports Server (NTRS)

The fluorometric gas-phase hydrogen peroxide procedure is based on the technique used by Lazrus et. al. for the determination of H2O2 in the liquid phase. The analytical method utilizes the reaction of H2O2 with horseradish peroxidase and p-hydroxphenylacetic acid (POPHA) to form the fluorescent dimer of POPHA. The analytical reaction responds stoichiometrically to both H2O2 and some organic hydroperoxides. To discriminate H2O2 from organic hydroperoxides, catalase is used to preferentially destroy H2O2. Using a dual-channel flow system the H2O2 concentration is determined by difference.

Kok, Gregory L.; Lazrus, Allan L.

1986-01-01

427

Gas-Phase Molecular Dynamics: Theoretical Studies In Spectroscopy and Chemical Dynamics  

SciTech Connect

The main goal of this program is the development and application of computational methods for studying chemical reaction dynamics and molecular spectroscopy in the gas phase. We are interested in developing rigorous quantum dynamics algorithms for small polyatomic systems and in implementing approximate approaches for complex ones. Particular focus is on the dynamics and kinetics of chemical reactions and on the rovibrational spectra of species involved in combustion processes. This research also explores the potential energy surfaces of these systems of interest using state-of-the-art quantum chemistry methods, and extends them to understand some important properties of materials in condensed phases and interstellar medium as well as in combustion environments.

Yu H. G.; Muckerman, J.T.

2012-05-29

428

Automated Resistivity Monitoring of Free Phase Gas Dynamics in a Northern Peatland  

NASA Astrophysics Data System (ADS)

Peatlands are sinks of atmospheric carbon dioxide, yet release large amounts of methane to the atmosphere. The net effect of this interchange is not well understood. Some conceptual models indicate steady diffusion and ebullition of methane from shallow peat dominates atmospheric fluxes, while others suggest episodic ebullition events from deep peat dominate methane emissions. Studies have demonstrated the effectiveness of various geophysical techniques to monitor changes in free phase gas content in peat. To better understand the mechanisms of free phase gas production in peat, we have established an autonomous DC resistivity monitoring system as part of the second year of a multi-scale, multi-method study within Caribou Bog, an ombotrophic patterned peatland located in Maine. DC resistivity is a readily automated imaging method, well suited for long-term studies of free phase gas dynamics below ground. Assuming negligible variation in fluid conductivity, changes in resistivity can be attributed to increases or decreases in gas content. Our system gathers data at approximately 4-hour intervals on a grid of 72 electrodes at 1.5 m separations and covering an area of 336 m^2. Full reciprocal datasets are also recorded for error analysis. Four vertical electrode arrays were installed from zero to 6 m depth within the grid and sampled multiple times daily over a period of 2 weeks using a Wenner configuration for validation of inversion results. To help identify forcing mechanisms on gas release, temperature, pressure, and pore fluid specific conductance are continuously recorded from sensors at various depths within the study area. Using a differencing inversion scheme, we identified small but significant changes in resistivity over time in response to gas build up, redistribution and release. These changes were particularly notable in the upper peat, where our models show localized shifts in resistivity of over 25% within one day. In addition, vertical radar profiles compare well with surface resistivity and build confidence in our results. Changes in pressure and water table depth recorded concurrently suggest that these variables partly regulate migration and release of free phase gas in peat. These geophysical data offer support for shallow peat as a major source of methane flux to the atmosphere. (a) comparison of apparent resistivity recorded from vertical array # 1 and horizontally averaged resistivity inversion results from surface electrodes in the region of the vertical array, (b) baseline log resistivity values from surface electrode dataset, (c) differences in resistivity after 1 day, (d) differences in resistivity after 5 days.

Terry, N.; Slater, L. D.; Sharma, S.; Lewis, E.; Comas, X.; Schafer, K. V.; Reeve, A. S.

2012-12-01

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